Autothermal Operation Research Articles

Characterization of a highly integrated, natural convection-driven, condensing methanol reactor

A highly integrated, natural convection-driven, condensing methanol reactor with the catalyst bed, heat integration section and liquid product separation in a single pressure vessel without moving parts is successfully tested. Space-time yields of up to 600kgMeOHmcat.−3h−1 are demonstrated, comparable to other CO2-to-methanol processes. The internal recycle by natural convection is successfully achieved as well as significant heat integration. A further reduction of heat losses to the environment is needed for autothermal operation. The dynamic characteristics of the process, with fast start-up times, a high turn-down ratio add to the potential to deal with intermittent feed supply. Overall the LOGIC 2.0 reactor concept is a promising process configuration for green methanol production.

Design and Development of Integrated Direct Air Capture and Methanation Processes

AbstractThe synergies from integrating direct air capture and CO2 methanation are assessed and quantified. Three direct air capture and methanation processes with different integration strategies are proposed: only heat integration, direct air capture sorbent regeneration with high‐pressure H2, and complete integration in a single unit. The heat integration study via pinch analysis evaluated the potential energy demand reduction. Overall autothermal operation is achievable, as the heat generated in methanation often exceeds that required for direct air capture sorbent regeneration. A novel process combining CO2 adsorption and methanation in one reactor provided the best productivity and energy demand results. However, this design requires complex cycles and strict demands on the sorbent and catalyst, requiring further development and experimental demonstration.

Biomass source influence on hydrogen production through pyrolysis and in line oxidative steam reforming.

This study evaluates the potential of several biomasses differing in nature and composition for their valorization by pyrolysis and in-line oxidative steam reforming. The first task involved the fast pyrolysis of the biomasses in a conical spouted bed reactor at 500ºC, in which product yields were analyzed in detail. Then, the oxidative steam reforming of pyrolysis volatiles (gases and bio-oil) was approached in a fluidized bed reactor. The reforming experiments were performed at 600 ºC, with an steam/biomass (S/B) ratio of 3 and catalyst (Ni/Al2O3) space times of 7.5 and 20 gcat min gvol-1. Concerning equivalence ratio (ER), a value of 0.12 was selected to ensure autothermal operation. Remarkable differences were observed in H2 production depending on the type of biomass. Thus, pine wood led to a H2 production of 9.3 wt%. The lower productions obtained with rice husk (7.7 wt%) and orange peel (5.5 wt%) are associated with their higher ash and fixed carbon content, respectively, which limit the efficiency of biomass conversion to bio-oil. However, in the case of the microalga, the poor performance observed is due to the lower conversion in the reforming step toward gases due to the composition of its pyrolysis volatile stream.

Resistive Heating Catalytic Micro-Reactor for Process Intensified Fuel Reforming to Hydrogen

Abstract Process intensification of fuel reforming using micro-reactors has become crucial for feed flexibility in H2 production for fuel cells. In the literature on microreactors, energy supply for these endothermic reactions has faced limitations, relying on external heating, or autothermal operation. This paper explores a novel approach using a thin-film catalytic heater to develop micro-reactors. The study focuses on dry methane reforming in a simplified micro-reactor where thermal energy is supplied through electric resistive heating of a thin carbon sheet with a catalyst applied to its surface. The thin catalytic heated layer inside the reactor minimizes energy losses and the reactor footprint. Power input was varied from 90-225 W to understand its impact on the reactor temperature, CH4 conversion, H2 and CO yields. Fast thermal response times were achieved using the carbon paper as thin film for heating. Ni/MgO impregnated onto carbon paper was utilized as the catalytic heating element which resulted in CH4 conversions greater than 60% at temperature above750 K. Influence of operating conditions such as the input molar ratio of CO2/CH4, and gas hourly space velocity (GHSV) were also investigated to understand the scope of the catalyst in this setup. High GHSVs (592,885 and 948,617 mL/(hr.gcatalyst)) were tested to understand the throughput achievable using this setup. This approach demonstrates improved scope and feasibility for further intensification compared to conventionally heated microreactors. The research paves the way for efficient and compact micro-reactors for fuel reforming processes.

Enabling plastic waste gasification by autothermal chemical looping with > 90 % syngas purity for versatile feedstock handling

The chemical looping gasification of plastics (CLGP) is a process that offers an innovative solution for transforming post-consumer waste plastics into high-value products. The process utilizes a co-current moving bed reducer reactor with iron-titanium-based oxygen carriers to gasify plastic feed and generate syngas autothermally. Its distinguishing feature is its ability to operate over a wide range of feed loadings and co-injection of mixed plastic species without any performance losses. Isothermal bench-scale experiments reveal a syngas purity of ∼95 %, aligning with the thermodynamic simulations. The moving bed reactor facilitates a deeper reduction of the oxygen carriers to the Fe+FeTiO3 phase, leading to the high syngas purity, which is then verified with additional TGA, XRD, and SEM analysis. For an autothermal operation of CLGP process, an active material content of 20 % is found to be sufficient to satisfy the kinetic and thermodynamic constraints. Further integration with downstream production of H2 is presented and compared to a steam gasification process. The process integration simulations show that the CLGP process outperforms the steam gasification system in terms of Cold Gas Efficiency (CGE), Effective Thermal Efficiency (ETE), and H2 yield. CO2 emissions are impressively reduced by ∼30 % in the CLGP system over that in the steam gasification system due to its ability to autothermally operate the process, unlike the highly endothermic steam gasification process.

Continuous wet air oxidation of aqueous phase from hydrothermal liquefaction of sewage sludge

The conversion of organic waste into advanced fuels through hydrothermal liquefaction (HTL) is a promising route. However, for the commercialisation of HTL technology, treatment and valorisation of the generated aqueous by-product are required for its economic viability. This study investigates subcritical non-catalytic continuous wet air oxidation (WAO) for the treatment of the aqueous phase from hydrothermal liquefaction (HTL-AP) of sewage sludge. A custom-made tubular reactor was used at temperatures and residence times similar to the HTL process (300–350 °C; 6–50 min), with excess air equivalent to 1.5–2 times the oxygen demand. The WAO process removed up to 95.3 % of the chemical oxygen demand and 91.8 % of the total organic carbon, generating volatile fatty acids, mainly acetic acid, as intermediary compounds from the oxidation reactions, and CO2 and H2O from the pollutant’s complete degradation. The process effectively eliminated almost all of the organonitrogen compounds, generating NH4+, which reached values of up to 97 % of the total nitrogen. Comprehensive molecular characterization performed by FT−Orbitrap MS analysis revealed that the main basic organonitrogen compounds in HTL-AP are distributed in the O1N1, N2, O1N2, N1 classes. For neutral to acidic organonitrogen species, O3N1 is the most representative chemical class. The energy consumption for heating the WAO reactor was up to 40 % lower using HTL-AP compared to blanks experiments. Despite good process water clean-up, autothermal operation was not achieved, and improvements in the reactor design are suggested.

Process efficiency and syngas quality from autothermal operation of a 1 MWth chemical looping gasifier with biogenic residues

Chemical looping gasification is a novel dual fluidized bed technology for the conversion of solid feedstock to a nitrogen-free syngas without the need of pure oxygen. While multiple electrically heated lab-scale experiments have been performed, data on gas quality including tars formed during operation have not been reported yet for autothermal process operation. In this study we present autothermal operation of a chemical looping gasifier with a thermal input in the 1MWth range, utilizing two circulating fluidized bed reactors with foresting residue and industrial wood pellets as feedstock and Norwegian ilmenite as bed material. A cold gas efficiency of around 50% was achieved in the non optimized pilot plant, indicating that higher values can be reached in a commercial unit when minimizing heat losses. The carbon conversion was around 90%, and this value is expected to increase to almost 100% when raising the temperature, residence time, and cyclone efficiency in a commercial unit. The syngas has a very high quality with methane concentrations in the range of 7vol.-% to 10vol.-% and gravimetric tar content below 1g/Nm3 measured via tar protocol.

Green hydrogen production from biomass – A thermodynamic assessment of the potential of conventional and advanced bio-oil steam reforming processes

Steam reforming of bio-oil derived from biomass pyrolysis is one of the most promising methods for the production of green hydrogen with minimal carbon footprint. In this context, this work investigates the thermodynamic potential of hydrogen production from bio-oil steam reforming. Four routes – conventional steam reforming (CSR) and three advanced reforming processes – sorption-enhanced steam reforming (SESR), chemical looping steam reforming (CLSR) and sorption-enhanced chemical looping steam reforming (SE-CLSR) - were modeled for this purpose. Bio-oil was modeled as a complex mixture of model compounds belonging to all major oxygenate families in order to have a closer resemblance with raw bio-oil. CaO was selected as the sorbent, while NiO was selected as oxygen carrier. Furthermore, the effect of process parameters such as steam to carbon, sorbent to carbon, oxygen carrier to carbon ratios, and reforming temperature was explored. H2 purity and yield along with energy demand, served as the parameters for comparing the performance of the four processes. SESR provided the highest H2 yield (0.216 kgH2 kgBio-oil−1) among all the processes under optimum conditions along with a purity greater than 99 %. CLSR, meanwhile, had the lowest H2 yield and purity (0.178 kgH2 kgBio-oil−1 and 64.6 %, respectively). The combined SE-CLSR process had H2 yield greater than both CSR and CLSR (0.197 kgH2 kgBio-oil−1) and a H2 purity greater than 99 %. High in-situ heat generation was noted in the reforming reactor for both SESR and SE-CLSR, pointing towards a good potential for auto-thermal operation. Overall, SE-CLSR process is a highly intensified process with substantially lower energy requirements than all the other processes. The results highlight that by combining CO2-sorption and chemical looping with traditional reforming, H2 can be obtained in higher yields and purity and lower energy consumption.

Carbon‐negative syngas production: A comprehensive assessment of biomass pyrolysis coupling chemical looping reforming

AbstractThis article introduces a pyrolysis chemical looping reforming (PCLR) process that produces carbon‐negative syngas in autothermal operation. To enhance the system's carbon negativity, a process configuration with oxygen carrier two‐stage regeneration is adopted, enabling internal CO2 utilization. The PCLR process is systematically evaluated and compared to chemical looping gasification and steam gasification processes in the process performance, energy efficiency, and environmental impact using a process model. Results reveal significant improvements over chemical looping gasification, including 69%, 45%, and 4% improvement in syngas yield, energy efficiency, and environmental benefit. Process analysis demonstrates that decoupling volatile reforming from pyrolysis and combustion enhances syngas quality, energy efficiency, and process flexibility. While the two‐stage regeneration sacrifices syngas production, it contributes to a 4% increase in carbon negativity and a 15% reduction in carbon emissions. Thus, the PCLR process effectively overcomes the limitations of chemical looping gasification systems and exhibits excellent process intensification performance.

Steps to understand the role played by the main operating conditions in the oxidative steam reforming of biomass fast pyrolysis volatiles

Biomass pyrolysis and in-line catalytic oxidative steam reforming of the volatiles (P-OSR) has been analyzed in a two-step reaction system made up of a conical spouted bed reactor (CSBR) and a fluidized bed reactor (FBR). A novel O2 multi-point injection system has been designed in order to ensure suitable O2 distribution in the FBR, and hence avoid the formation of hot spots that may lead to irreversible catalyst deactivation by metal sintering. Optimization of the main process parameters has been approached in order to maximize H2 production and overcome the high energy requirements of the endothermic reforming reaction. The study has been conducted in the following ranges of the operating conditions: Reforming temperature, 550–700 °C; space time, 5–20 gcat min gvolatiles−1; steam/biomass (S/B) ratio, 2.5–5; and equivalence ratio (ER) from 0 to 0.19. Moderate reforming temperatures (600–650 °C), a S/B value of 3 and a space time of 15 gcat min gvolatiles−1 are the optimum conditions for the process. Furthermore, when low space time values are used, O2 feeding rates into the reforming step of up to an ER value of 0.12 (corresponding to autothermal operation (ATR)) revealed a synergistic effect promoting reforming reactions. Thus, an improvement in H2 production from 6.81 wt% to 8.26 wt% was observed by changing ER from 0 to 0.12, which means H2 production increases by 21.4% compared to the conventional pyrolysis-reforming (P-SR) process. Therefore, the promising results obtained in this study prove the suitability of the continuous P-OSR strategy for H2 production from biomass and involve a step forward towards the scaling up of the process.

Strong ectopic adsorption on single cobalt site accelerates the direct catalytic oxidation of low concentration acetonitrile on CuO nanoparticles embedded in SAPO-34

It is usually inevitable for the usage of zeolite rotor concentrator to increase the level of volatile organic compounds (VOCs) concentration, which in turn enables the regenerative catalytic oxidation of VOCs with large gas flow rate to achieve autothermal operation. Herein, we present a new strategy for the preparation of autothermal oxidation catalyst (AOC) with strong ectopic adsorption ability for VOCs molecules by the on-site doping of single cobalt sites on CuO nanoclusters confined in zeolitic materials SAPO-34, which exhibits a strong enrichment ability for low concentration acetonitrile even at 300 °C. Meanwhile, a distinguished enhancement on the catalytic oxidation activities has also been achieved according to the formation of CoⅡ-oxo and/or Co-Ovac sites on CuO nanoparticles.

Depleted uranium oxide supported nickel catalyst for autothermal CO2 methanation in non-adiabatic reactor under induction heating

Undoped nickel-based catalysts supported on depleted uranium oxide allow one to carry out CO2 methanation process under extremely low reaction temperature under atmospheric pressure and powered by a contactless induction heating. By adjusting the reaction conditions, the catalyst is able to perform CO2 methanation reaction under autothermal process operated inside a non-adiabatic reactor, without any external energy supply. Such autothermal process is possible thanks to the high apparent density of the UOx which allows one to confine the reaction heat in a small catalyst volume in order to confine the exothermicity of the reaction inside the catalyst and to operate the reaction at equilibrium heat in-heat out. Such autothermal operation mode allows one to significantly reduce the complexity of the process compared to that operated using adiabatic reactor, where complete insulation is required to prevent heat disequilibrium, in order to reduce as much as possible, the heat exchange with the external medium. The catalyst displays an extremely high stability as a function of time on stream as no apparent deactivation. It is expected that such new catalyst with unprecedented catalytic performance could open new era in the field of heterogeneous catalysis where traditional supports show their limitations to operate catalytic processes under severe reaction conditions.

Design and control concept of a 1 MWth chemical looping gasifier allowing for efficient autothermal syngas production

Chemical looping gasification (CLG) is a novel gasification concept, allowing for the efficient production of a high calorific, N₂-free syngas with low tar content. Previous studies showed that the inherent process characteristics require a dedicated process control concept in order to allow for sufficient solid and thus heat transport between the two reactors (air and fuel reactor) of the gasification unit, while at the same time being able to accurately tailor the air-to-fuel equivalence ratio (λ), thus obtaining stable gasification conditions. To demonstrate its viability, a suitable control concept was implemented in the 1 MWth modular pilot plant located at the Technical University Darmstadt. In this paper, results obtained during the first ever autothermal CLG operation, achieved in this unit using biomass pellets as the feedstock, are presented, highlighting important process fundamentals. It is demonstrated that the novel process control concept allows for an accurate control of λ in semi-industrial scale, while at the same time guaranteeing stable hydrodynamics and thus solid and heat transport between the air and fuel reactor, making it a suitable control concept for large-scale implementation. Moreover, it is demonstrated that the underlying phenomena of the CLG process lead to substantial system inertia, as the solid bed inventory of the gasifier acts as an oxygen storage during transient periods, evoked by changes in the air-to-fuel equivalence ratio.

Experimental demonstration of 80 kWth chemical looping combustion of biogenic feedstock coupled with direct CO2 utilization by exhaust gas methanation

Chemical looping combustion is a highly efficient CO2 separation technology without direct contact between combustion air and fuel. A metal oxide is used as an oxygen carrier in dual fluidized beds to generate clean CO2. The use of biomass is the focus of current research because of the possibility of negative CO2 emissions and the utilization of biogenic carbon. The most commonly proposed OC are natural ores and residues, but complete combustion has not yet been achieved. In this work, the direct utilization of CLC exhaust gas for methane synthesis as an alternative route was investigated, where the gas components CO, CH4 and H2 are not disadvantageous but benefit the reactions in a methanation step. The whole process chain, the coupling of an 80 kWth pilot plant with gas cleaning and a 10 kW fluidized bed methanation unit were for this purpose established. As OC, ilmenite enhanced with limestone was used, combusting bark pellets in autothermal operation at over 1000 °C reaching high combustion efficiencies of up to 91.7%. The fuel reactor exhaust gas was mixed with hydrogen in the methanation reactor at 360 °C and converted with a methane yield of up to 97.3%. The study showed especially high carbon utilization efficiencies of 97% compared to competitor technologies. Based on the experimental results, a scale-up concept study showed the high potential of the combination of the technologies concerning the total efficiency and the adaptability to grid injection.Graphical

Oxidative fast pyrolysis of biomass in a quartz tube fluidized bed reactor: Effect of oxygen equivalence ratio

The effect of oxygen equivalence ratio (ER) on oxidative fast pyrolysis of pine sawdust was investigated in a quartz tube fluidized bed reactor. The results showed that the introduction of oxygen into fluidizing gas would mainly oxidize the biochar, thus provided the largest contribution to heat demand during biomass pyrolysis towards autothermal operation. The increase of ER from 0 to 11.15% decreased the biochar yield from 21.03 to 9.5 wt%. The enthalpy for fast pyrolysis of pine sawdust was about 1084.49 kJ/kg, and a theoretical ER to achieve autothermal pyrolysis was thus calculated as ∼3.92%. The addition of oxygen indeed changed the formation and distribution of bio-oil. With ER of 6.47%, although the bio-oil yield decreased slightly, the light compounds in bio-oil (e.g., linear alcohols/carbonyls/acids, furan compounds and cyclopentanones/cyclohexanones) were largely consumed, while the heavy compounds (e.g., phenols/aromatic hydrocarbons and anhydrosugars) were mostly retained with the formation of anhydrosugars being promoted.

The effect of ferrous sulfate pretreatment on the optimal temperature for production of sugars during autothermal pyrolysis

Fast pyrolysis is a promising technology for producing cellulosic sugars from lignocellulosic biomass. Success in this endeavor requires measures that prevent naturally occurring alkali and alkaline earth metals (AAEM) from breaking pyranose and furanose rings in lignocellulosic biomass. This is especially critical for high ash feedstocks like corn stover and other kinds of herbaceous biomass. Pretreating corn stover with ferrous sulfate converts AAEM into thermally stable salts, which passivates the catalytic activity of these metals and dramatically improves sugar yields. AAEM passivation in combination with autothermal (partial oxidative) operation improves the prospects for intensifying the production of sugars via fast pyrolysis. We hypothesized that pretreated biomass pyrolyzed in the presence of oxygen can substantially influence the temperature dependence of pyrolysis kinetics. We found that autothermal (air-blown) pyrolysis of ferrous sulfate pretreated corn stover achieved maximum sugar yield of 15.6 wt% (biomass basis) at 450 °C, whereas the maximum phenolic oil yield of 9.2 wt% (biomass basis) was reached at 500 °C. Considering these tradeoffs in yields of these highly desirable pyrolysis products, the ideal operating temperature is between 450 and 500 °C. These results suggest that two-stage pyrolysis might allow maximum recovery of both sugars and phenolic oil.

Scale-up analysis of the oxidative dehydrogenation of ethane over MoVTeNbOx catalysts in an autothermal reactor

We examine the oxidative dehydrogenation of ethane (ODHE) using a one-dimensional finite heat dispersion model and present a comprehensive ignition-extinction analysis of the process in an adiabatic autothermal reactor. The six-step kinetic model used in the scale-up studies was derived from lab-scale reactor data and validated over a wide range of experimental conditions. We investigate the impact of ethane to oxygen feed ratio, space time, and bed length on the region of autothermal operation as a function of feed temperature. The results reveal that ethane conversion and ethylene selectivity are not monotonic at the extinction point and there exists an optimum set of design and operating conditions. We also report the impact of operating pressure in terms of fixed linear and mass velocities. Our analysis and comparisons show that ODHE, when operated at high pressure, may lead to performance that is comparable to the ethane steam cracking process.

Computational study of the segmental catalysis of steam-methanol reforming in heat integrated microchannel reactors for hydrogen production

The present study focuses upon segmentally catalyzed steam-methanol reforming processes for producing hydrogen in heat integrated microchannel reactors. Computational simulations are carried out to understand the causes of the fundamental phenomena involved in segmental catalysis and the autothermal operation. The benefits of segmental catalysis are discussed, and some aspects of heat phenomena are explained. The effects of wall thermal conductivity, flow velocity, and catalyst segment thickness are evaluated to determine how to design heat integrated reactors for specific operations by tailoring segmental catalysis approaches. To understand the importance of thermal management, the phenomena of heat in the catalyst structure are discussed in terms of anisotropic thermal conductivity and reaction heat flux. The results indicate that the benefits of segmental catalysis are surprisingly great. Segmental catalysis can be applied to greatly extend the operation regime, and the segmented oxidation design offers distinct advantages. The segmented design may offer improvements in heat and mass transport but presents thermal management challenges caused by the rapidly varying concentrations and temperatures. The wall thermal conductivity is vital in achieving heat balance and high process efficiency. Transverse wall heat conduction is of especially critical importance in thermal management. The flow velocity and catalyst segment thickness are of great importance to the improvement of conversion and productivity. An optimum flow velocity for highest overall performance exists.

Solid flux measurement in dual fluidized bed processes based on solid samples

Chemical looping gasification is a novel dual fluidized bed technology for the conversion of solid feedstock to a nitrogen-free syngas without the need of pure oxygen. Recently, a pilot plant has been erected to advance chemical looping gasification towards autothermal operation. For autothermal operation, the solids flux between the two reactors becomes important, as it transports the required sensible heat in addition to the oxygen required for the process. As a reliable method to accurately measure the solids flux under process conditions currently does not exist, a method has been devised to measure the solid circulation for dual fluidized bed systems and tested utilizing the process specifics of chemical looping gasification to allow for calibration of online measurement equipment without opening the reactor system. This method utilizes solid samples from coupling elements to calculate the solids flux in chemical looping gasification with an overall uncertainty smaller than 20%.

Design and performance analysis of a solar dual fluidized bed gasifier

The potential to conduct allothermal steam-gasification of biomass using a dual fluidized bed gasifier (DFBG) assisted by solar energy has already been conceptually proposed. In this paper the design and operation of a solar DFBG (SDFBG) device to deal with this concept is assessed by modeling, considering thermodynamic, kinetic and fluid-dynamic issues. The challenges identified in previous works, as well as the modifications required in the current state-of-the-art technologies of (no-solar) DFBG for implementing the new solution using heated particles as heat carriers, are worked out. Two SDFBGs, considering different arrangements for integrating the solids carrying the solar energy into the system, are designed. The operation of both under different solar-external heat loads, from autothermal operation (no external heat) to 3 MJkgbio,daf−1 of external heat, is assessed and compared. This work shows how the technology can be implemented and scaled up.