Autothermal Operation Research Articles

Auto-thermal operation and optimization of coal-fueled separated gasification chemical looping combustion in a pilot-scale unit

As one of the chemical looping combustion (CLC) technologies, separated gasification-CLC (SG-CLC) can realize the carbon separation during coal combustion process with low degradation of oxygen carrier and high performances. In order to realize the auto-thermal operation of the constructed pilot-scale SG-CLC unit, some oxygen was added into the gasification agent to compensate the endothermic gasification of coal using steam. The combustion performances of SG-CLC unit were investigated under different conditions with variables of reaction temperature, coal feed rate, steam mass flow, oxygen flow and type of loosen gas. Ten conditions were designed and conducted to study the effects of variables on the CLC performances. According to the temperature curves, auto-thermal operation was achieved in seven of these tests. Carbon capture efficiencies under auto-thermal operation were almost higher than 97% and the oxygen demands in these test were less than 4.70%. The peak value of solid fuel conversion was 93.91% at 930 °C while the minimum was 87.36% at 830 °C under auto-thermal conditions. The performances demonstrated that the SG-CLC system could offer great possibility for its commercial application under auto-thermal conditions. Furthermore, some measures were put forward to optimize the operation of this SG-CLC system.

Compact Steam-Methane Reforming for the Production of Hydrogen in Continuous Flow Microreactor Systems

The implementation of fuel cell deployment requires efficient conversion of fuels into hydrogen in a distributed energy system. Fortunately, continuous flow and microreactor technology provide unique opportunities for the portable production of hydrogen. This study focuses on determining the operation space for a thermally integrated methane reforming system, thereby providing a theoretical basis for the design and optimization of such systems. The steam-methane reforming over rhodium coupled with methane combustion over platinum in a thermally integrated microchannel reactor arranged with rectangular-shaped protuberances was studied numerically in order to improve its operability and stability. Computational fluid dynamic simulations were carried out with detailed reaction mechanisms to identify conditions for the maximum hydrogen yield and the highest output power. Various operating lines were presented, and various performance metrics were evaluated accordingly. The results indicated that the efficient production of hydrogen is made possible through improving transport performance for highly active catalysts. The flow disturbance elements designed for the reactor are of great benefit to intensification of the reforming process. There exists a trade-off between fuel utilization and output power. Autothermal operation advantages from improved transport performance in small physical dimensions were demonstrated for the system, but careful thermal management is always necessary to ensure its efficient and stable operation. The thermal conductivity of the wall separating the exothermic and endothermic reactions plays a significant role in determining the performance of the system. Highly active catalysts are required to intensify the overall reforming process and to achieve efficient thermal management. Adjustment of fluid velocities can serve as a convenient means to achieve efficient operation of the system.

Experimental Research on the Thermal Oxidation of Ventilation Air Methane in a Thermal Reverse Flow Reactor.

The thermal reverse flow reactor is an effective technical equipment for dealing with ventilation air methane, which has been causing a significant greenhouse effect. An experimental study on the thermal oxidation of ventilation air methane in a thermal reverse flow reactor was conducted. A mixture of domestic gas and ambient air was used to simulate ventilation air methane in the experiments, and the methane conversion efficiency was analyzed based on the concentration of combustion products determined by gas chromatography equipment. In addition, the effects of the switching time, the inlet methane concentration, the flow rate, and heat extraction were studied. The experimental results show that the reverse flow reactor system can run under a wide range of operating conditions with autothermal operation and high methane conversion. In addition, this system can even work with methane concentrations as low as 0.30% in the autothermal operation mode without NOx emission. Unlike previous studies, this study shows that the flow rate has little effect on the methane conversion rate in the cyclic steady state over a wide range of operating conditions. In addition, methane conversion and reaction zone change as the inlet methane concentration varies during the reaction process in the cyclic steady state. The combined optimization of operating parameters can effectively improve the stability of the reverse flow reactor system and methane conversion efficiency.

Reduction Kinetics of Perovskite Oxides for Selective Hydrogen Combustion in the Context of Olefin Production

Chemical looping represents a novel approach for generating light olefins in which thermal cracking or catalytic dehydrogenation is coupled with selective hydrogen combustion (SHC) by a metal oxide redox catalyst, which enables autothermal operation, increased per‐pass conversion, and greater‐than‐equilibrium yields. Recent studies indicate that Na2WO4‐promoted perovskite oxides are effective redox catalysts with high olefin selectivity. Herein, kinetic parameters, rates, and reaction models for the reduction of unpromoted and Na2WO4‐promoted CaMnO3 redox catalysts by H2, C2H4, and C2H6, is reported. Reduction rates of CaMnO3 under ethylene and ethane are significantly lower than under H2. Model fitting of reduction kinetics show good agreement with reaction order–controlled models for CaMnO3 reduction and predict greater oxygen site dependence and higher activation energy for CaMnO3 reduction by C2H4 as compared with H2. Avrami–Erofe'ev nucleation and growth models provide the best fit to the reduction of Na2WO4/CaMnO3 in H2 and in C2H4. After Na2WO4 promotion, the reduction rate of CaMnO3 is three orders of magnitude lower in ethylene in comparison to hydrogen, consistent with its superior selectivity to hydrogen combustion. The models developed can be applied toward reactor design and optimization in the context of enhanced olefin production via SHC under a cyclic redox scheme.

Making Fuel on Mars: Methane Synthesis from Martian-Derived CO2 and H2o Using a Sabatier Electrolyzer Based on Proton-Conducting Ceramics

We present our development of dense proton-conducting ceramic membranes to synthesize CH4 and O2 from CO2 and H2O feed streams. The National Aeronautics and Space Administration (NASA) seeks such technology to enable manned missions to Mars. The CO2 and H2O feedstocks are in abundant supply on the Red Planet; solar power can be harnessed to convert these feedstocks via electrochemical reactors into fuels and O2 to sustain human life and enable permanent bases. NASA’s current approach features a two-stage process that starts with H2 synthesis through solar-driven H2O electrolysis using polymer-electrolyte membranes (PEM) at ~ 100 °C. The H2 product is then mixed with CO2 drawn from the Martian atmosphere and fed to a separate reactor held at ~ 400 °C in which a ruthenium catalyst promotes the Sabatier reaction to form methane: CO2 + 4 H2 → CH4 + 2 H2O This two-stage process joining a steam electrolyzer with a Sabatier reactor results in high conversion of CO2 and reasonable rates of CH4 production. However, the PEM-based H2O electrolysis suffers from low efficiency, resulting in an energy-intensive CH4 and O2 production. Our work seeks to combine these two processes into a single Sabatier Electrolyzer reactor based on proton-conducting ceramic membranes. Like PEMs, proton-conducting ceramic membranes transport reasonable rates of H+ ions at lower overall cell voltages due to increased temperature operation and low overpotentials for H2O splitting. The decreased electric power requirements for the Sabatier Electrolyzer are further enabled by autothermal operation where the Ohmic heating maintains the cell at the necessary temperatures for high H+ conduction and effective Sabatier chemistry (~ 400 °C). Integration of the catalyst with the electrolyzer simplifies the system, improves reliability, and provides increased performance within a smaller package. Figure 1 illustrates the Sabatier Electrolyzer concept. Martian derived H2O and CO2 are fed to opposing electrodes of a protonic-ceramic electrolysis cell. Steam is electrolyzed (top) with the product O2 exhausting from the cell. The product protons are driven across the protonic-ceramic membrane to the fuel electrode, where they react with CO2 to form CH4 and H2O. The combination of processes can match the exothermicity of CO2 hydrogenation with the endothermicity of H2O electrolysis, promoting thermal balance and high efficiency. This novel process intensification of intermediate temperature H2O electrolysis with Sabatier chemistry brings many questions. For example, do the protons crossing the membrane directly react with CO2 at the fuel electrode (as shown in Figure 1), or do they recombine to form H2 that subsequently reacts with CO2 within the nickel-laden fuel electrode to form CH4? What are the optimal operating conditions for integrating the protonic-ceramic electrolyzer with the Sabatier chemistry? What performance and reliability can NASA expect from a protonic-ceramic Sabatier Electrolyzer, in terms of electrical efficiency, methane production per unit mass, and long-term stability of cell voltage and current? CSM researchers have previously demonstrated encouraging results with proton-conducting ceramics for a number of applications, including electric-power generation and fuels synthesis. In this presentation, we will review our efforts to extend development of protonic-ceramic cells to the Sabatier Electrolyzer shown in Figure 1. The cells feature a BaCe0.2Zr0.6Y0.2O3-d (BCZY26) electrolyte, a Ni-BCZY26 fuel electrode support, and a BaCo0.4Fe0.4Zr0.1Y0.1O3-d (BCFZY) steam electrode. Results will be presented for CO2 conversion and CH4 selectivity under electrolysis operation. Figure 1

Evaluation of a new DCFB reactor system for chemical looping combustion of gaseous fuels

A 120 kWth chemical looping combustion pilot plant, has been used to evaluate the performance of up to 10 different oxygen carrier materials within more than 1000 h of operation. It was one of the largest pilot plants, featuring a scale up ready design and auto thermal operation. Initially the plant was designed for nickel based oxygen carriers. During the evaluation of other materials, limitations of the reactor design caused by different design demands of the oxygen carriers have been identified. A new reactor system has been installed incorporating design adaptations to improve the reactor flexibility and performance. The new air reactor is narrower and allows higher gas velocities and high solid circulation rates, even at lower fuel loads. The upper loop seal, connecting the air reactor with the fuel reactor has been optimized to reduce a gas leakage between the reactors, identified in the old reactor system. The new fuel reactor consists of two sections, a lower part with a larger cross section and a narrower upper part. This allows larger specific inventories in the reactor and good gas/solid contact over the full reactor height. The new reactor system has been evaluated during a benchmark campaign, using a manganese based oxygen carrier which has also been used in the old unit. The results are reported in this work. The new design meets the design criteria, high solids circulation is possible, higher specific inventories can be operated and the gas leakage via the upper loop seal has been reduced significantly.

Mapping the operating performance of a novel internally circulating fluidized bed reactor applied to chemical looping combustion

Chemical looping combustion is a promising technology for minimizing the energy penalty of CO2 capture. To accelerate the scale-up and commercialization of this technology for pressurized operation, the internally circulating reactor (ICR) was recently proposed. ICR integrates the two reactors, cyclones, loop seals and solids transport lines of the conventional chemical looping configuration into a single unit that simplifies design and operation. This work reports the ICR operating performance over a range of operating parameters applied to chemical looping combustion (CLC). The concept proved relatively simple to operate, allowing the oxygen-carrier circulation rate to be controlled over a wide range by varying the bed loading and the air reactor feed rate. Fully autothermal CLC operation was demonstrated as an illustration of the ease of ICR operation. Gas leakage between the two reactor chambers decreased strongly with decreasing solids loading, resulting in CO2 capture and purity up to 94% for the lowest bed loading. The data showed that significant room for further optimization of the solids transport ports in the reactor exists, which will further increase the CO2 separation performance. These results demonstrate the promise of ICR concept and provide valuable insights for the design of larger-scale units in future work.

Conventional and autothermal pyrolysis of corn stover: Overcoming the processing challenges of high-ash agricultural residues

The high ash content of agricultural residues and other kinds of herbaceous biomass makes it a challenging feedstock for fast pyrolysis to bio-oil. Using corn stover as a representative feedstock, this study investigates fast pyrolysis of high ash, herbaceous biomass in a pilot-scale fluidized bed reactor using both conventional, nitrogen-blown and autothermal, air-blown operation. Initial efforts to pyrolyze corn stover were challenged by bed fouling, which prevented steady reactor operation. Substitution of coarser bed material allowed operation at higher superficial velocities, which promoted attrition and elutriation of recalcitrant biochar particles from the reactor. This resulted in dramatic improvement in stable reactor operation for both conventional and autothermal pyrolysis with bio-oil yields among the highest reported for pyrolysis of corn stover. The oxygen-to-biomass equivalence ratio required for autothermal operation was 6.8%. Autothermal operation also resulted in significant process intensification, increasing corn stover throughput from 7.8 kg hr−1 to 21.9 kg hr−1 for this 8.9 cm diameter reactor. Air-blown, autothermal operation did not significantly reduce bio-oil yield despite the presence of partial oxidation reactions. Carbon balances indicate carbon yields of biochar and aqueous, bio-oil light ends decreased by 18.5% and 4.7%, respectively, during autothermal pyrolysis compared to conventional pyrolysis while the more valuable, organic-rich heavy ends of the bio-oil were essentially preserved.

Microstructured Fischer‐Tropsch Reactor Scale‐up and Opportunities for Decentralized Application

AbstractCurrent projects focusing on the energy transition in traffic will rely on a high‐level technology mix for their commissioning. One of those technologies is the Fischer‐Tropsch synthesis (FTS) that converts synthesis gas into hydrocarbons of different chain lengths. A microstructured packed‐bed reactor for low‐temperature FTS is tested towards its versatility for biomass‐based syngas with a high inert gas dilution. Investigations include overall productivity, conversion, and product selectivity. A 60‐times larger pilot‐scale reactor is further tested. Evaporation cooling is introduced which allows to increase the available energy extraction from the system. From that scale on, an autothermal operation at elevated conversion levels is applicable.

An advancement in CO2 utilization through novel gas switching dry reforming

This study is the first experimental demonstration of CO2 capture and utilization for dry methane reforming using a novel chemical looping concept, “Gas Switching Dry Reforming” (GSDR) to produce syngas. The new reactor concept utilizes a single fluidized bed reactor to complete redox (reactions) cycles by alternating air and gaseous fuel feeds, generating heat and near pure CO2 for usage in a consecutive dry reforming stage. Autothermal operation of GSDR was achieved using NiO/Al2O3 oxygen carrier, in a three-stage configuration where pure CO is used in the reduction stage while CH4 and CO2 are fed simultaneously in the reforming stage. Most of the heat duties of the process is generated by the exothermic oxidation reaction. The reforming stage is very sensitive to temperature with very good CH4 and CO2 conversion achieved at 850 °C but dropped rapidly at lower temperatures. Carbon deposition is a major issue affecting the performance of GSDR process although this is found to be minimized by a combination of high operating temperature and larger CO2/CH4 ratio, but also led to low H2/CO molar ratio driven by the reversed water gas shift reaction. Reducing the utilization of the oxygen carrier by 50% also proves to decrease carbon deposition by 62% due to the presence of latent oxygen on the oxygen carrier. However, CH4 and CO2 conversion are affected negatively resulting in a drop of ∼22%. An excellent opportunity for maximizing the energy efficiency of the GSDR is by integration with a Gas-To-Liquid (GTL) Fisher Tropsch to use outlet gas stream from the reforming as feedstock to GTL while the unconverted hot gasses from GTL process is fed to the reduction stage of GSDR.

Autothermal reactor design for catalytic partial oxidations

A comprehensive analysis of the impact of various design and operating variables on the boundary of the region of autothermal operation of type III is presented. It is shown that for a fixed adiabatic temperature rise and space time, the largest region of autothermal operation is obtained in the homogeneous limit (small particles or high cell density monoliths) when the bed scale heat Peclet number approaches zero, mass Peclet number approaches infinity, and with smaller bed aspect ratios (height to diameter). For competing multiple oxidation reactions, while thin (shallow) beds could lead to larger region of autothermal operation, better selectivity of intermediate product may be attained using very thin beds. The impact of heat loss on the region of autothermal operation is also analyzed. When inter and intra-phase heat and mass transfer gradients are significant so that particle (channel) level ignition could occur, autothermal operation is feasible for any bed level heat Peclet number with reactor operated in the mass transfer controlled regime. The results of the analysis are applied to two processes of interest, namely, oxidative coupling of methane (OCM) with adiabatic temperature rise in the range 600–1200 K and catalytic partial oxidations (CPO) with adiabatic temperature rise in the range 200–500 K. For OCM, some feasible autothermal reactor designs that are suitable for different catalyst activity levels are proposed. For CPO, an autothermal reactor design is compared favorably to the traditional cooled multi-tubular reactor.

Operation of a 50-kWth chemical looping combustion test facility under autothermal conditions

The United States Department of Energy is developing transformational fossil fuel combustion technologies that result in more efficient power cycles and/or substantial reductions in GHG emissions. Chemical Looping Combustion (CLC) has the potential to achieve a lower cost of electricity than a supercritical pulverized coal power plant with an amine absorption system. Although the concept and research on chemical looping has a long history, CLC has numerous technical issues that must be addressed prior to a commercial debut. This effort is directed toward the following major issues for CLC: (1) demonstrating continuous solids handling, operability, and reactor performance at autothermal conditions and (2) preliminary assessments of oxygen carrier attrition and relative material make-up costs. These are critical issues that should be addressed under realistic conditions prior to directing resources toward larger scale demonstrations. This paper will also describe NETL’s small 50-kWth natural gas circulating CLC test facility located in Morgantown, WV. Despite its small size, this experimental test unit has operated at autothermal conditions for 11 h using a copper-iron-alumina oxygen carrier developed at NETL. This paper will describe the test facility and operating experiences using NETL’s “Gen 2.0” oxygen carrier material. Natural gas conversion to CO2 ranged from 70 to 90% over approximately 75 oxidation-reduction cycles during the autothermal operating period. Estimates for the process specific attrition rate during autothermal operation are also presented. Finally, estimates for the oxygen carrier makeup cost, specific to the NETL process configuration, are several orders of magnitude greater than the NETL target. Future work should focus on reducing the oxygen carrier material cost and improving the attrition resistance of the oxygen carrier material under autothermal test conditions.

Thermochemical assessment of chemical looping assisted by oxygen uncoupling with a MnFe-based oxygen carrier

A previously developed manganese-iron mixed oxide doped with TiO2 shows promising properties for the combustion of solid fuels with intrinsic CO2 capture by Chemical Lopping assisted by Oxygen Uncoupling (CLaOU) owing to its oxygen uncoupling capability, i.e. ability to generate gaseous oxygen at high temperature, and to oxidize gaseous fuels such as H2, CO or CH4 by reacting with lattice oxygen. In this work, a window of suitable operating conditions was determined to facilitate the use of this material in a CLaOU unit. For this purpose, mass and enthalpy balances were performed for the whole CLaOU unit considering theoretical values of thermochemical parameters, such as the equilibrium constant of relevant reactions in CLaOU and the formation enthalpies of reacting solids. An air reactor temperature of 1148 K and a high air excess ratio are suggested in order to promote the transfer of oxygen via the oxygen uncoupling mechanism, which would be preferable for the combustion of solid fuels. Auto-thermal operation of the CLaOU unit is guaranteed for air excess ratio values λ < 3. The fuel reactor temperature is highly influenced by the oxygen carrier-to-fuel ratio (ϕ) and the oxygen carrier regeneration in the air reactor. Assuming a 50–75% regeneration of the oxygen uncoupling capability, and ϕ = 4–6, the fuel reactor temperature would be between 35 and 50 K above the air reactor temperature. The higher temperature in the fuel reactor could promote the fuel conversion, while oxygen carrier regeneration would be guaranteed by the lower air reactor temperature.

Process intensification of biomass fast pyrolysis through autothermal operation of a fluidized bed reactor

Heat transfer is the bottleneck to fast pyrolysis of biomass. Although the enthalpy for pyrolysis of biomass is relatively small operation at temperatures around 500 °C constrains heat carrier selection to inert gases and granular media that can sustain only modest thermal fluxes in practical pyrolysis systems. With heat transfer controlling the rate of pyrolysis, reactor capacity only scales as the square of reactor diameter and does not benefit from economies of scale in building larger reactors. We have eliminated this heat transfer bottleneck by replacing it with partial oxidation of pyrolysis products to provide the enthalpy for pyrolysis in a fluidized bed reactor, a process that can be described as autothermal pyrolysis. The oxygen-to-biomass equivalence ratio depends upon the kind of biomass being pyrolyzed and the level of parasitic heat losses from the reactor, but under conditions that simulate adiabatic operation, equivalence ratios are around 0.10, compared to 0.20 or higher for autothermal gasifiers. At this low equivalence ratio, there was no significant loss in bio-oil yield when operating the reactor autothermally (64.8 wt%) as compared to conventional pyrolysis (64.4 wt%). Carbon balances indicate that less valuable pyrolysis products (char and aqueous, bio-oil light ends) are consumed via partial oxidative reactions to provide the enthalpy for pyrolysis. While the carbon yields of char and bio-oil light ends decreased by 25.0% and 21.3%, respectively, the most valuable pyrolysis product (bio-oil heavy ends) only decreased 8.0%.

Simplified model of torrefaction-grinding process integrated with a power plant

A simple method is presented to formulate the total energy consumption of a biomass torrefaction process operating as a standalone unit or integrated with a downstream power plant. New expressions are derived to estimate the volatiles heating value, mass yield at autothermal operation, and mass yield at minimum energy consumption. Experimental data reported in the literature for grinding torrefied beech in a knife-mill are correlated to estimate the specific grinding energy. The presented model accurately predicts the critical moisture content and the auxiliary heat input of a 150 MWth torrefaction plant producing torrefied woodcutting. Illustrative numerical results are presented for an integrated application using willow and beech as two woody feedstocks. The autothermal solid yield is found to be higher than that at optimum energy consumption. The autothermal solid yield declines with moisture content and it is approximately the same for both feedstocks. For every percentage point increase in the power plant efficiency, the optimum solid yield increases 0.67% and 0.15% for willow and beech, respectively, whereas the energy consumption decreases by 7.1 kJ/kg (willow) and 5.75 kJ/kg (beech). The results suggest that the design of torrefaction plants is highly feedstock-dependent. The method presented can be applied to any type of feedstock and both upstream and downstream applications. It is a simple and effective tool that can be used to have a quick estimate of optimum operating point and energy consumption at early design stages.

Gas Switching Reforming (GSR) for syngas production with integrated CO2 capture using iron-based oxygen carriers

The process behavior of a Gas Switching Reforming (GSR) reactor was studied using three different iron-based oxygen carrier materials: Iron-oxide on Alumina, Iron-Nickel oxide on Alumina and Iron-Ceria on Alumina. It was observed that, for all oxygen carriers, the fuel stage reaction occurs in two distinct sub-stages when feeding methane and steam to a bed of oxidized material, with methane combustion dominating the first and methane reforming dominating the second. This reflects a change in the catalytic activity of the oxygen carrier as it is reduced. The alumina support was observed to play a significant role in the reactions occurring, with the redox-active phases being hematite-structured Fe2O3 (oxidized form) and spinel-structured (FeNiAl)3O4 (reduced form).The Nickel-containing oxygen carrier outperformed the others in the reforming sub-stage, showing 40% improved methane conversion. The feed of dry methane only during the combustion sub-stage was found to improve methane conversion to syngas in the subsequent reforming sub-stage from 75% to 80% at 800 °C. Results also show that methane conversion improves with the increase in operating temperature and steam/carbon ratio. Autothermal operation of the reactor was achieved with repeatable performance over several redox cycles. The study therefore successfully demonstrated autothermal N2-free syngas production with integrated CO2 capture from the fuel combustion required to supply heat to the endothermic reforming reactions.

Hydrogen production from bio-oil: A thermodynamic analysis of sorption-enhanced chemical looping steam reforming

The steam reforming of pyrolysis bio-oil is one proposed route to low carbon hydrogen production, which may be enhanced by combination with advanced steam reforming techniques. The advanced reforming of bio-oil is investigated via a thermodynamic analysis based on the minimisation of Gibbs Energy. Conventional steam reforming (C-SR) is assessed alongside sorption-enhanced steam reforming (SE-SR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR). The selected CO2 sorbent is CaO(s) and oxygen transfer material (OTM) is Ni/NiO. PEFB bio-oil is modelled as a surrogate mixture and two common model compounds, acetic acid and furfural, are also considered. A process comparison highlights the advantages of sorption-enhancement and chemical looping, including improved purity and yield, and reductions in carbon deposition and process net energy balance.The operating regime of SE-CLSR is evaluated in order to assess the impact of S/C ratio, NiO/C ratio, CaO/C ratio and temperature. Autothermal operation can be achieved for S/C ratios between 1 and 3. In autothermal operation at 30 bar, S/C ratio of 2 gives a yield of 11.8 wt%, and hydrogen purity of 96.9 mol%. Alternatively, if autothermal operation is not a priority, the yield can be improved by reducing the quantity of OTM. The thermodynamic analysis highlights the role of advanced reforming techniques in enhancing the potential of bio-oil as a source of hydrogen.

Internally circulating fluidized-bed reactor for syngas production using chemical looping reforming

Chemical looping reforming (CLR) is a promising method for achieving autothermal methane reforming without the energy penalty of an air separation unit that is required for partial oxidation (POX) or oxygen-blown autothermal reforming (ATR). Scale-up of the conventional dual circulating fluidized bed CLR configuration is challenging, however, especially under the pressurized operating conditions required for high process efficiency. The internally circulating reactor (ICR) concept has previously been proposed as a simplified solution for chemical looping, especially under pressurized operation. It assembles the chemical looping process into a single reactor with two sections connected by specially designed ports for oxygen carrier circulation. This study has successfully demonstrated CLR operation in a dedicated ICR test unit with a NiO oxygen carrier. Up to 3 kW of methane feed was reformed to syngas, achieving conversion efficiencies as high as 98%. The reactor behaved largely as expected over a range of CH4/O2 ratios and in a case with steam addition. Autothermal reactor operation could also be achieved, illustrating the practicality of the ICR concept. Based on this positive first demonstration study, further study of the ICR concept is recommended.

Analysis of Combined Biochar and Torrefied Biomass Fuel Production as Alternative for Residual Biomass Valorization Generated in Small-Scale Palm Oil Mills

From the residual biomass generated by the palm oil sector in Ecuador, kernel shell (KS) is of major importance because it has been demonstrated that its use as solid fuel could replace diesel and LPG currently subsidized by the government to be used in the industrial and commercial sectors to produce thermal energy. The implementation of a torrefaction process could improve the KS handling and transportation operations, thus promoting its domestic use. However, the mesocarp fiber (MF) generated in the mills is 2.5 times the amount of KS generated. Therefore, this work analyzes an energy system that could valorize simultaneously MF and KS by the integration of pyrolysis and torrefaction processes, to produce biochar and torrefied fuel. A numerical model is used to analyze the integration of the pyrolysis and torrefaction processes considering a temperature range between 250 and 550 °C. It is observed that biochar and torrefied fuel could be produced simultaneously from pyrolysis process temperatures of 460 °C. The maximum load capacity of the integrated pyrolysis and torrefaction system corresponds to the highest temperature considered 550 °C (1 kg of KS per each kg of MF). However, the highest energy efficiency is found at lower pyrolysis process temperatures, near the auto-thermal operation temperature. The average efficiency of the analyzed energy system is 59.7%. Thus, the use of an integrated pyrolysis and torrefaction system could be an efficient alterative to be applied in small scale mills, to improve the KS energy density and valorize MF into biochar.

High-Pressure Chemical Looping Reforming Processes: System Analysis for Syngas Generation from Natural Gas and Reducing Tail Gases

Reforming technologies produce syngas that serves as an important intermediate in the production of fuels and chemicals in the chemical and petrochemical industry. Only recently has reforming technology based on the chemical looping concept been attempted. Most chemical looping studies have been performed under ambient pressure conditions, but most processes that use syngas operate at an elevated pressure. Understanding the effect that pressure has on syngas generation in a chemical looping reactor is essential to the design of the overall system. This study characterizes and compares the effect of pressures on syngas yields under various chemical looping reforming operating conditions. Specifically, in this study, an iron-based oxygen carrier is used for the chemical looping partial oxidation reaction of methane to form syngas. The equilibrium simulation is of direct relevance to process applications, as demonstrated by the methane and metal oxide co-current reactor system, where in previous studies, experimental product yields were shown to be appropriately represented by equilibrium conditions. The results of syngas generation at 1 atm are used in this study as the basis for comparison to those obtained under pressurized conditions. The isothermal syngas generation is first examined qualitatively and quantitatively for pressures ranging from 1 to 30 atm. The adiabatic syngas generation is then examined under autothermal operating conditions. The sensitivity studies are performed to describe the changes in product yields as the temperature and pressure along with steam and CO2 inputs are varied. The results of the analysis illustrate the various competing factors that dictate the high-pressure syngas yield and purity. The study also provides insight into choice of operating conditions that enable thermodynamic syngas yields at higher pressure to be comparable to those at atmospheric pressures.