Complete Carbon Conversion Research Articles

Study of the influence of external heat and mass exchange on the features of combustion and extinction of gas suspensions of carbon particles

In the work, the regularities of the influence of heat and mass exchange of gas suspensions of carbon particles with the external gas environment on the processes of ignition, burning and quenching at different mass concentrations of carbon fuel are studied. A monodisperse gas suspension of carbon particles located in a gas heated to a high temperature, which contains an oxidant, is considered. As a result of the conducted physical and mathematical modeling, the following characteristics of high-temperature processes were determined: induction period, burning time and time of complete transformation of particles, critical parameters of ignition and extinction of particles. The influence on these characteristics of the initial particle diameter, mass concentration and temperature of the surrounding gas was analyzed. It was found that the external heat and mass exchange has a slight effect on the induction period and critical parameters of the ignition of gas suspensions, but it has a sufficiently strong effect on the characteristics of the combustion and extinguishing processes. The existence of an upper limit for fuel concentrations and particle diameters at which complete combustion of gas suspensions is not observed in the absence of external mass transfer is proved. Ranges of mass concentrations were found for which complete conversion of carbon fuel burning in the form of gas suspensions is carried out. It is shown that for open gas suspensions, the range of mass concentrations, where complete transformation of particles is observed, expands to the side of large values. The diameters of the particles characterizing the quenching of gas suspensions, taking into account the external mass transfer, are smaller, as a result of a greater supply of oxygen to the volume of the gas suspension.

Integration of thermal plasma with CCUS to valorize sewage sludge

The presented study addresses the threefold challenges namely, sustainable waste valorization of a difficult waste stream, climate change due to CO2 emissions and clean energy crisis and it is a small step forward to achieve SDG-7. A hybrid DC thermal plasma was employed in a pilot scale facility (∼150 kW) to treat sewage sludge in the presence of waste CO2 (according to the concept of CCUS, Carbon Capture Utilization and Storage) to produce syngas and assess the viability to retrieve phosphorus and other valuable materials from the generated ash. An equilibrium model was also developed to enhance the understanding about the dynamics of process. The H2 generation was around 0.5 m3/kg fuel whereas the amount of char produced was negligible (0–0.013 kg/kg fuel) realizing an efficient transformation of carbon. It was promising to find a high amount of P2O5 in the ash retained in the filter (30 wt %) and reactor (9 wt %) as evaluated by XRF. An average value of 97 % was obtained for CCE (carbon conversion efficiency) depicting almost complete carbon conversion. The results are encouraging to valorize sewage sludge under the CCUS scheme to produce clean energy and reclaim valuable nutrients.

The Realization of complete carbon conversion and hydrogen purification in the coal-fueled chemical looping technology using a cost-effective iron-based oxygen carrier

The development of cost-effective and reactive oxygen carriers and the fast and complete conversion of solid fuels are two critical issues in the solid fuel chemical looping technology. Red mud, a solid waste from the alumina industry, was found to be an economic oxygen carrier candidate simultaneously realizing the use of solid wastes and the CO2 abatement after comparing with other two different iron-based materials (pure Fe2O3 and hematite). This study validated red mud as an excellent oxygen carrier to achieve the almost complete conversion of char in solid fuels (SFs) (99.4%) and meanwhile the hydrogen production with high-purity (97% H2 purity) and higher H2 yield (around 500 mL/g), in the optimized pyrolysis procedure of solid fuels with proper gasification agent and rationalized reaction temperatures (1000 °C) and residence time (10mins). Characterizations of red mud using SEM-EDS and XRD revealed that the unique microscopic crystalline structures of both Fe2O3 and Ca2Al2SiO7 particles nested on Na4Al2Si2O9 molten substrate, implying that the existence of Na-containing component of the red mud OC likely accounts for its higher reactivity and stability in multiple redox cycles.

Experimental investigation on carbon microstructure for coal gasification in supercritical water

Supercritical water gasification of coal (SCWGC) has great potential for converting coal into CO2 and H2 effectively and environmentally. For a better technological competitiveness, the conversion mechanism of carbon structure needs to be investigated in depth to achieve 100% carbon conversion for SCWGC under mild conditions. Ningxia anthracite (NX), Hongliulin bituminous coal (HLL) and Zhundong lignite (ZD) were selected as feedstock to investigate the carbon microstructure evolution for different ranks of coal gasification in supercritical water (SCW). Raman and XRD spectra were employed to investigate the carbon microstructure information of solid residues. The experimental results illustrated that coal rank had slight effect on the evolution law of carbon microstructure in coal. The process of SCWGC included three stages depending on the characteristic reactions. Inhibiting the condensation of aromatic rings under 550–750 °C in the third stage was the key to effectively control the ordered conversion and achieve complete conversion of carbon in the coal. Besides, the Raman and XRD spectral parameters had close relationship with carbon gasification efficiency, respectively.

Coupling CO2 utilization and NO reduction in chemical looping manner by surface carbon

Carbon deposits typically enforce shutdowns of chemical reactors to periodically regenerate their active materials, a continuous challenge for industry and scientists alike. This downside can however be turned to benefit by utilizing carbon’s reductive power. Here, we integrate dry reforming of methane (DRM) and selective reduction of nitric oxide (SRN) in a novel chemical looping process, coupled by the periodic deposition and removal of surface carbon, which participates in both reactions. Carbon formed on the catalyst during dry reforming is subsequently used as reductant for nitric oxide (NO) conversion into N2, hence not only achieves stable CO2 utilization and NO reduction with cyclic catalyst regeneration, but also reduces the consumption of valuable energy resources demanded by NO removal. In contrast to co-feeding all reactants in a single step, the inherent temporal-spatial separation of reactions in chemical looping allows for complete conversion of carbon and NO, ensuring a higher exergetic efficiency (70 % more efficient). Also, adaptation of the relative duration of the DRM and SRN steps to the conditions of the CO2 and NO industrial point sources allows to account for the differences in supply of carbon and NO, offering an attractive strategy for selective catalytic reduction of NO with greenhouse gases rather than NH3.

Process modelling for the production of hydrogen-rich gas from gasification of coal using oxygen, CO2 and steam reactants

This process modelling studied the effect of different reactants on syngas composition and gasifier heat duty (heat energy required to carry out the operation) and the downstream treatment of CO rich syngas to maximise hydrogen yield. The process modelling was validated against experimental data obtained from a large bench-scale entrained flow gasifier. Results show that considering the H2/CO ratio, the steam-O2 reactant favours the most compared to those of the pure oxygen and oxygen-CO2 reactants. Under comparable operating conditions, the highest H2/CO ratio of 0.74 was determined using steam-O2 reactant compared to that of 0.31 and 0.33 using steam-CO2 and pure oxygen reactant. The catalytic water-gas shift reaction (WGSR) favours the yield of H2 with complete CO conversion at a temperature of 400 °C using the steam/coal ratio of 1.2. Supplying steam in the gasifier requires more heat energy to be supplied to drive endothermic gasification reaction and maintain the gasifier temperature. Under complete carbon conversion, steam-CO2 and steam-oxygen reactants require 5–65 kW more energy than pure oxygen.

Evaluation of high-temperature pyrolysis and CO2 gasification performance of bituminous coal in an entrained flow gasifier

This study used an entrained flow gasifier to assess the pyrolysis and gasification performance of Bangladeshi Barapukurian bituminous coal. The pyrolysis and CO2 gasification were conducted at temperatures of 1000°C–1400 °C under atmospheric pressure. The carbon conversion, syngas yield and pollutant emissions of coal using two different particle size of 90–106 and 250–300 μm have been analysed under CO2 concentration of 10–80 vol%. Solid residue (char/ash) was analysed by using scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) methods. Results show that the release of volatile matter increases up to the temperature of 1200 °C. However, the temperature needs to increase at 1400 °C for the complete carbon conversion. Based on the CO/H2 ratio, syngas conditioning is required while using a temperature of 1200 °C or above, especially over the stoichiometric CO2 concentrations. Considering the heating value of syngas for power generation, the use of CO2 should be limited to less than 20% at a temperature of 1200–1400 °C. Particle size is important for carbon conversion but there is no significant impact on the heating value of syngas. Installation of the syngas cleaning system is required to drop the pollutants emission from the ppmv range to the ppbv range.

Interpreting biomass gasification histories with CBK/G. Part 2. Extrapolations to entrained-flow gasification conditions

This study characterizes how biochars’ distinctive kinetics affect the predicted performance of a pilot-scale oxygen-blown, entrained-flow biomass gasifier, where temperatures and pressures are much greater than those in the laboratory database used to assign kinetic parameters in Part 1. The gasifier operates at pressures of 0.2 and 0.7 MPa, temperatures from 1050 to 1550 °C, stoichiometric ratios from 0.25 to 0.50, and firing rates from 200 to 600 kW. Predicted product gas compositions are generally accurate to within 2% for CO and 4% for H2 across the testing domain with various raw and torrefied wood products. Fifty to 70% of the CO and 65 to 90% of the H2 in the syngas form during the reforming of volatiles along with the combustion of small amounts of char and soot during the early stages while O2 is still present. Among diverse biomass forms, the crucial kinetic parameter assignment is the activation energy for oxide desorption. High energies extrapolate to nearly complete carbon conversion and nearly uniform CO levels across a broad range of SR. Low energies extrapolate to much lower carbon conversions and a corresponding fall-off in CO levels for progressively greater SR. Only biochars with the highest energies for oxide desorption have the potential to give more soot than char in their unconverted carbon emissions. This paper also presents a quantitative evaluation of extrapolated CBK/G kinetics with measured temperatures of individual particles for two gasification conditions in a lab-scale burner at 1600 °C.

Recent advances in diesel autothermal reformer design

The autothermal reforming of diesel fuel is a catalytic process that runs at temperatures of 700 °C–900 °C. Long-chain hydrocarbon molecules react with steam and O2, yielding a product gas that mainly consists of CO, CO2, CH4 and H2. H2 is essential for the operation of fuel cell systems. The Forschungszentrum Jülich has been engaged in the cooperative development of technical apparatus for this reaction to be applied in fuel cell systems over the past 15 years, together with many other research groups worldwide, and this paper deals with reactor ATR 14, which is considered the preliminary end-product of Jülich's research and development in this field. This paper briefly summarizes Jülich's earlier reactor generations and then describes the most recent improvements embodied in the ATR 14. Additionally, the experimental evaluation of the ATR 14 is presented, which demonstrates that it can be operated over a broad load range and with almost complete carbon conversion.

Production of a fuel gas by fluidised bed coal gasification compatible with CO2 capture

A continuously fed, laboratory scale spouted bed gasifier has been used to study oxy-fuel gasification of German lignite. In this paper, the influence of different gasification agents and bed temperature on the process performance, during tests at atmospheric and elevated pressure are studied. Two gasification agents have been used, CO2 (with different CO2/C ratios) and mixtures of CO2/steam. The results show that despite the relatively slow CO2-char reaction, good gasification performance could be achieved with German lignite by adjusting the operating conditions at atmospheric pressure: complete carbon conversion, high energy conversion and a medium heating value fuel gas (8–10 MJ m−3). The CO2/C ratio was found to have a large effect on the gasification performance. Increasing the ratio increased the carbon conversion, but the CO2 conversion decreased. At 950 °C, maximum carbon conversion was already achieved with pure CO2, therefore using steam at this temperature could not increase the conversion, but did increase the H2/CO ratio in the fuel gas. At 850 °C, replacing 25% of CO2 with steam increased the carbon conversion to the level achieved at 950 °C without steam. Replacing more than 25% of CO2 with steam increased the H2/CO ratio further. Therefore, with the addition of steam, the operating temperature could be reduced from 950 °C to 850 °C while maintaining the gasification performance. The changes of gasification performance with steam addition at pressures up to 10 bara followed the same trends achieved at atmospheric pressure.

Premilinary Results: Heterogeneous Reaction of Epoxidation Palm Kernal Oil

The epoxidized vegetables oils can be used a raw material for a broad range of products, from pharmaceutical and plastics to paint and adhesives. Epoxidation of oleic acid was carried out by using hydrogen peroxide as an oxygen donor and formic acid as an oxygen carrier in the presence of sulphuric acid act as catalyst. The crude oleic acid contained 75% oleic acid, 12.2% linoleic acid, 6.5% palmitic acid and 7.5% stearic acid, and had an iodine value of 98.99 g/100 g. The epoxidation of oleic acid with almost complete conversion of unsaturated carbon and negligible oxirane cleavage can be obtained by the in situ techniques. An analytical approach for the prediction of the partition coefficient for formic acid between oleic acid and water, dependent on temperature and composition, has been proposed.

Determination of the kinetic constants of the process of plasma gasification of coal-water fuel

The chemical kinetics of processes of thermal transformations of carbon-containing media was studied at high-temperature processing (2000 K ≤ T ≤ 5000 K) in the chamber of a plasma-jet reactor using water vapor as an oxidizer. The chemical reactions rate was calculated according to the method of determining the kinetic constants of the process of gasification of coal-water fuel. The influence of the temperature of the gaseous environment in the chamber on the time of complete carbon conversion of the fuel particles is established. An example of calculating the parameters of the gasification process of coke residue particles with a size of (5 - 20)·10-5 m with an oxidizer excess coefficient α = 0.45 and fuel consumption mf = 100 kg/hr is given. The expediency of the process of vapor-plasma gasification at the temperature of gases in the reactor chamber up to 3000 K is shown.

Fate of a biomass particle during CO2 gasification: A mathematical model under entrained flow condition at high temperature

The gasification reactions of solid carbonaceous particles such as biomass or coal are complex. Multiple physical phenomena and operating conditions of gasifier simultaneously govern the response of these reactions during carbon conversion. Direct or indirect coupling among the involved transport mechanisms of heat and mass transfer and the chemical kinetics at the active site of the solid impact the overall gasification performance. This study addresses a mathematical model during CO2 gasification of a spherical biomass particle subject to entrained flow condition at high temperature. An algorithm is developed to account both internal and external mass transport limitation during char conversion while devolatilization event occurs in parallel. The prediction of overall carbon conversion is compared to experimental data from a bench scale entrained flow reactor. The results show almost 60% devolatilization is completed when the char gasification reaction starts and the char conversion is <0.8% when the particle is completely devolatilized. The effect of the boundary layer is important during the devolatilization event that provides heat and mass transfer resistance. Complete carbon conversion for 90 μm particle can be achieved at 1200 °C temperature and 40% concentration of CO2 with a time close to 10 s.

Gas production from polyethylene terephthalate using rotating arc plasma

Polyethylene terephthalate (PET) is one of the most widely used macromolecule materials, but the treatment of waste PET has been a great challenge to environment safety. In this article, we report for the first time an effective method to produce gaseous products containing acetylene, ethylene and carbon monoxide from PET particles using a rotating direct current arc plasma reactor. Thermodynamic simulation was performed, and the effect of input power, PET feed rate and working gas flow rate on PET pyrolysis was experimentally investigated. An almost complete carbon conversion could be achieved by this method with a product gas containing 42% acetylene, 53% carbon monoxide and 4% ethylene, while the specific energy consumption of product gas was below 20 kWh/kg. These results show that rotating arc plasma is a promising method of improving the conversion of waste PET to valuable hydrocarbons and syngas.

Interaction of diesel engine soot with NO2 and O2 at diesel exhaust conditions. Effect of fuel and engine operation mode

This work shows a study of the reactivity of twelve different types of soot with either NO2 or O2 under reacting conditions typically present in diesel particulate filters (DPFs). The soot samples were obtained from the combustion of four conventional and alternative fuels (diesel, biodiesel and two paraffinic fuels) in a diesel engine bench operated under three different engine operation modes: a typical urban-driving mode and two variations to this mode to assess the effect of the injection settings. The main objective of the work is to relate the oxidative reactivity of the soot to the nature and the origin of each sample. The possible simultaneous elimination of soot and NOx at typical diesel exhaust conditions is examined, as well. The reactivity tests were performed in a laboratory quartz gas flow reactor, discontinuous for the solid. The soot-NO2 interaction was studied with 200 ppm of NO2 at 500 °C and the soot-O2 interaction was studied with 5% O2 at 500 °C and 600 °C. The experimental results were used to determine the time needed for the complete conversion of carbon (τ) through the use of the equations of the Shrinking Core Model for solid-gas reactions with decreasing size particle and chemical reaction control. In general, the τ values show that the diesel fuel generates a less reactive soot than biodiesel or the alternative paraffinic fuels. In addition, increasing the injection pressure or adding a post-injection to the original injection strategy generates a more reactive soot. These findings point out that there is potential to achieve efficient regeneration processes in DPFs through other fuels than conventional ones and via engine calibration.

Influence of Different Pretreatment Methods on Biomass Gasification and Production of Fischer-Tropsch Crude Integrated with a Pulp and Paper Mill

In this paper, the influence on the system performance of different biomass pretreatment methods before gasification and subsequent production of Fischer-Tropsch crude is considered. Entrained flow gasification at high pressure is a well proven technology for coal as feedstock with the benefit of producing a practically tar free raw gas with a close to complete carbon conversion. The short residence time in this type of gasifier requires a fuel, which is relatively dry and has a small particle size, to be pressurized from ambient conditions up to 20-50 bar. The small particle size can be acquired by grinding but this is highly energy intensive and feeding is challenging. Torrefaction is a thermal pretreatment method carried out at around 300 °C which makes the biomass easier to grind, thus requiring less electricity, and makes the material less fibrous, while on the other hand requiring heat for the process. Pyrolysis is a process carried out at around 500 °C which lets the biomass decompose into a gaseous, a liquid and a solid part. The solid part can be grinded and fed into the gasifier together with the liquid and gaseous phases. This will further facilitate the feeding but with a further increased heat demand compared to torrefaction. The different pretreatment methods and their impact on the overall biorefinery energy system have been studied and evaluated using process integration methodology. The results show that the excess heat from an FT process with a biomass input of 300 MW(HHV) can replace the solid fuel boiler in a large chemical pulp and paper mill. With the preconditions given for this study, thermal pretreatment of the biomass can be beneficial in terms of system thermal efficiency.

Pyrolysis of Polyolefins Using Rotating Arc Plasma Technology for Production of Acetylene

Polyolefin, as one of the most widely used macromolecule materials, has been one of the most serious threats to the environment. Current treatment methods of waste polyolefin including landfill, incineration, and thermal degradation have suffered from severe problems such as secondary pollution and the generation of other toxic substances. In this article, we report for the first time a high-efficiency method to produce high-value C2H2 from polyolefins using a rotating direct current arc plasma reactor, using polyethylene and polypropylene as feedstocks. The essence of this method is that a reductive atmosphere of pyrolysis enables a thermodynamic preference to C2H2 over other carbon-containing gas and the rotating direct current arc plasma reactor allows for a uniform distribution of high temperature to ensure high conversion of polymers. Thermodynamic simulation of product composition was performed, and the effect of plasma input power, polyolefin feed rate, and working gas flow rate on the pyrolysis results was experimentally investigated. It was found that, with proper parameter control, approximately complete conversion of carbon in polyolefin could be obtained, with a C2H2 selectivity higher than 80% and a C2H2 yield higher than 70%. These results not only create new opportunities for the reuse of polymer waste, but are also instructive for the green production of C2H2.

Conversion of glycerol into syngas by rotating DC arc plasma

One of the most stable byproducts of biodiesel industry is glycerol, for which there’s lack of a large-scale application currently. Thermal plasma treatment is a potentially viable means of recycling glycerol by converting it into syngas. In this work, a rotating DC arc plasma reactor was used to decompose glycerol in order to produce syngas. The effect of plasma input power, glycerol feed rate, and water content in feedstock on the syngas conversion was investigated. It was found that the product gas stream, on an argon-free basis, contained 38% CO and 56% H2, with the balance being methane, ethylene, and little C4 hydrocarbons. Complete carbon conversion and energy conversion efficiency of 66% could be obtained with sufficient input power. Water content of feedstock influenced the amount of CO and H2 in the product gas. Magnetic flux intensity of the reactor showed negligible effect on the composition of the product gas, carbon conversion and energy conversion efficiency, but could prevent the anode and plasma reactor from severe erosion.

Interaction of Soot–SO2: Experimental and Kinetic Analysis

ABSTRACTThis study aims to evaluate the capability of SO2 to interact with soot and to determine the kinetics of this reaction under conditions of interest for combustion. The conditions of the soot reactivity experiments were: 1% SO2 with nitrogen to balance, around 10 mg of soot, and different reaction temperatures for each run: 1275, 1325, 1375, 1425, and 1475 K. Results demonstrate that SO2 does interact with soot. The evaluation of the soot reactivity has been based on the calculation of the time for the complete conversion of carbon through the employment of the Shrinking Core Model equations for decreasing size particle with chemical reaction control. The reactivity of soot with SO2 increased by a factor of about 3 when increasing the reaction temperature of the test from 1275 K to 1475 K. Kinetics in terms of Arrhenius parameters showed that the activation energy of the interaction of soot with SO2 was around 82 kJ/mol.

In situ experimental study on the combustion characteristics of captured chars on the molten slag surface

Captured char particles on the molten slag continue to burn or transform into residual carbon in a slagging combustor or furnace, which affect the complete carbon conversion. This study applied a high temperature stage microscope to investigate the combustion behavior of captured chars on the molten slag surface. The combustion process of captured chars with air on the slag surface was observed and recorded, compared to the original char combustion. Particle size evolution calculated from the measured cross section area versus time indicated that the burnout time of chars was prolonged on the molten slag surface. Besides the heat transfer analysis also showed that the temperatures of char particles on the molten slag were decreased due to the thermal conduction between char and slag. Molten slag layer reduced the char reactivity from the analysis of combustibility index, indicating the captured char combustion on the molten slag surface was hindered. Coupled with heat transfer analysis, shrinking particle model (SPM) was applied and modified to predict the combustion time at carbon conversion of 0.9, and results showed an agreement with the experimental data.