Thermochemical Reactions Research Articles

EVALUATION OF THE EXHAUST FLUE GAS ENERGY THERMOCHEMICAL RECOVERY EFFECTIVENESS FOR A SUBMERGED GAS COMBUSTION MELTING FURNACE

One of the main indicators of the technological process perfection is the exhaust streams material and energy resources utilization degree. This is especially important for high-temperature processes with a high external energy consumption level in metallurgy, glass, mineral wool, etc. Traditional methods of exhaust heat utilizing to burner air heating by various recuperators designs provide a no more than 60 % heat recovery rate, mainly because of the limited recuperators materials heat resistance. Preliminary theoretical calculations and some available practical implementations experience indicate that with high-temperature exhaust gases (> 800 °C) the thermochemical method of their heat recovery becomes promising for the hydrocarbon fuels conversion, primarily natural gas methane, in order to obtain a higher-potential fuel with increased accumulated energy density. The efficiency of thermochemical recovery due to equipping a high-temperature submerged combustion melting furnace by exhaust gas temperature of at least 1200 °C with an additional thermochemical reactor were evaluated. Bibl. 16, Fig. 6, Tab. 3.

Heating of nanoparticles and their environment by laser radiation and applications

This review considers the fundamental dynamic processes involved in the laser heating of metal nanoparticles and their subsequent cooling. Of particular interest are the absorption of laser energy by nanoparticles, the heating of a single nanoparticle or an ensemble thereof, and the dissipation of the energy of nanoparticles due to heat exchange with the environment. The goal is to consider the dependences and values of the temperatures of the nanoparticles and the environment, their time scales, and other parameters that describe these processes. Experimental results and analytical studies on the heating of single metal nanoparticles by laser pulses are discussed, including the laser thresholds for initiating subsequent photothermal processes, how temperature influences the optical properties, and the heating of gold nanoparticles by laser pulses. Experimental studies of the heating of an ensemble of nanoparticles and the results of an analytical study of the heating of an ensemble of nanoparticles and the environment by laser radiation are considered. Nanothermometry methods for nanoparticles under laser heating are considered, including changes in the refractive indices of metals and spectral thermometry of optical scattering of nanoparticles, Raman spectroscopy, the thermal distortion of the refractive index of an environment heated by a nanoparticle, and thermochemical phase transitions in lipid bilayers surrounding a heated nanoparticle. Understanding the sequence of events after radiation absorption and their time scales underlies many applications of nanoparticles. The application fields for the laser heating of nanoparticles are reviewed, including thermochemical reactions and selective nanophotothermolysis initiated in the environment by laser-heated nanoparticles, thermal radiation emission by nanoparticles and laser-induced incandescence, electron and ion emission of heated nanoparticles, and optothermal chemical catalysis. Applications of the laser heating of nanoparticles in laser nanomedicine are of particular interest. Significant emphasis is given to the proposed analytical approaches to modeling and calculating the heating processes under the action of a laser pulse on metal nanoparticles, taking into account the temperature dependences of the parameters. The proposed models can be used to estimate the parameters of lasers and nanoparticles in the various application fields for the laser heating of nanoparticles.

Oriented radiation regulation via forward and backward scattering of foam structural catalyst in thermochemical reactor for enhanced solar to fuel conversion

Oriented radiation regulation via forward and backward scattering of foam structural catalyst in thermochemical reactor for enhanced solar to fuel conversion

Impact of cycling on the performance of mm-sized salt hydrate particles

Potassium carbonate is shown to be a promising salt for thermochemical heat storage. For a thermochemical reactor application, the salt hydrate is manufactured in mm-sized particles. It is known that salt hydrate particles undergo swelling and cracking during cyclic testing. Therefore, in this work the influence of cycling on structural and morphological evolution is investigated and the resulting impact on the hydration performance. It is found that the incremental volume increase during cycling is independent of the density at which a particle is produced. With lower starting relative density particles are found to be stable for more cycles compared to particles produced with high starting relative densities. Powder formation at the particle surface starts as soon as the particle density is close to values reported for percolation thresholds. The morphological changes during cycling result in formation of isolated pores and a highly tortuous pore system. As a result, the effective diffusion coefficient for cycled particles is lower compared to what is predicted for as produced particles with similar porosity resulting in lower power output than expected based on porosity. The results from this work help in understanding the reasons for swelling, cracking, powder formation and decreased performance with cycling, laying the foundation for mitigating these unwanted effects.

Kinetic modeling of thermal degradation of TDI/MDI-based flexible polyurethane foam under nitrogen and air atmospheres with Shuffled Complex Evolution algorithm: Insights from TG-FTIR analysis

This study investigates the thermal degradation mechanisms and kinetics of TDI/MDI-based flexible polyurethane foam (FPUF) under nitrogen and air atmospheres, employing thermogravimetric (TG) analysis in conjunction with TG-FTIR technique. The information gleaned from these analysis is used to construct kinetic model based on model-free approaches coupled with the Shuffled Complex Evolution optimization algorithm. The results uncovered the five-step complex thermal degradation process of TDI/MDI-based FPUF compared to TDI-based or MDI-based polyurethane in both atmospheres. In nitrogen atmosphere, this involve the dissociation of TDI- and MDI-based urethane bonds, breakage of recombined urea bonds, random chain scission of polyol, and further degradation of incompletely pyrolyzed solid products. In air atmosphere, the process emcompasses dissociation of TDI- and MDI-based urethane linkages, accelerated oxidation of polyol chains, consumption of urea groups, and combustion of partially oxidized intermediates. This work also emphasizes the limitations of solely relying on TG tests for kinetic modeling, necessitating the integration of TG tests and TG-FTIR technique to obtain a comprehensive understanding of degradation mechanisms. The significance of the acquired insights lies in their potential to reshape the design of thermo-chemical reactors, resulting in heightened resource recovery, diminished environmental impact, and a stride towards a circular economy within the polyurethane industry.

Control of strong electronic oxide-support interaction in iron-based redox catalysts for highly efficient chemical looping CO2 conversion

Moderating oxide/metal-support interactions over redox catalysts is effective way to achieve efficient chemical looping CO2 conversion, however, identify the interaction type, control the interaction intensity, and reveal its correlation with CO yield from a molecular perspective remain challenging. In this work, a crystal engineering strategy for tuning strong electronic interaction over Fe2O3/ZrO2 is reported and demonstrated by theoretical calculations, characterization techniques and reactivity evaluations. Compared to t-ZrO2, m-ZrO2 exhibits a stronger electronic interaction intensity with iron oxide and iron species as well as creates more oxygen vacancy and transfers more electrons to facilitate H2 and CO2 activations, which decreases the energy barriers of redox reactions. This mechanism makes Fe2O3/m-ZrO2 perform with two times higher of time-averaged CO space time yield (560 mmolCO·s−1·kgFe2O3−1) than Fe2O3/t-ZrO2. Electronic interaction intensity shows a positive relationship with CO yield. The findings provide a general guideline to rationally design efficient catalysts for thermochemical and redox reactions.

Experimental study of a high-temperature porous-medium filled solar thermochemical reactor for CO production

Solar thermochemistry via a two-step cycle has been considered as a promising technology as it is feasible to convert solar energy into fuels directly. The improvement of solar-to-fuel energy efficiency is strongly dependent on the heat recovery during the temperature swing between the reduction and oxidation steps. The present article describes the experimental results of a solar thermochemical reactor with gas-gas heat recovery. The reactor's inlet and outlet gases are exchanged through the heat exchanger, thereby improving the energy utilization efficiency, and a series of experiments are carried out to further demonstrate the feasibility of this technology. The influence of the pressure of the endothermic reduction step and the influence of the concentration of reactants in the exothermal oxidation step on the experimental results are analyzed. The experimental results show that vacuuming condition further promoted the reduction kinetics compared with Ar purging, and the yield of CO increases from 1.13 mL/gCeO2 to 1.32 mL/gCeO2 within 60 min. Therefore, the following experiments are completed under vacuuming condition for the endothermic reduction reaction. The yield of CO is favored at higher CO2 partial pressure, and the yield of CO increases from 44.65 mL to 279.42 mL as the volume flow rate of CO2 increase from 0.5 L/min to 4 L/min. This research provides useful information on the industrial implementation of the thermochemical technology.

Analysis of the possibility of solid-phase ignition of coal fuel

The article presents the results of theoretical and experimental studies of the ignition process of coal fuel particles in a pelletized state during high-temperature radiation-convective heating in an oxidizing environment. A new, different from the known, “two-temperature” mathematical model of the ignition process of a cylindrical coal pellet under intense heating conditions is presented. During the modeling, a detailed kinetic scheme of the reaction of gaseous products of thermal decomposition of coal with atmospheric oxygen was considered. The mathematical model was tested through a comparative analysis of the theoretical and experimental values of the ignition delay times of coal pellet fuel with experimental data. A wide range of heating conditions that could potentially lead to solid-phase ignition were analyzed. The research results showed that even under conditions of high oxygen content in the original coal, solid-phase ignition of coal pellets does not occur during intense heating. Based on the results of numerical modeling, it was established that the ignition process occurs in the gas phase. The oxygen released during the thermal decomposition of coal is not enough for stable gas-phase or heterogeneous ignition of pyrolysis products in the intrapore space of the fuel pellet. Based on the results of the numerical modeling, it was established that the oxygen released during the thermal decomposition of coal is significantly deficient in the intrapore space. The O2 concentration is not enough for a significant (in terms of heat flow) thermochemical intrapore reaction with gaseous and solid products of thermal decomposition.

Quantitative evaluation of radiative heat transfer from reactor surface to multiphase reaction medium in a supercritical water gasification reactor for coal

Supercritical water gasification (SCWG) of coal is a clean coal utilization technology, which converts organic matter in coal into hydrogen-rich gases through a series of thermo-chemical reactions. In this process, thermal radiation is an important heat transfer mechanism and significantly affects thermal efficiency and gasification performance. This paper aims to develop a comprehensive numerical model integrating with solving radiative transfer to precisely simulate the process of SCWG of coal, and quantitatively evaluate non-grey radiative heat exchange between reactor surface and multiphase reaction medium. The simulation results are validated against experimental data. It is shown that under practical operating conditions, thermal radiation accounts for 30 % – 42 % of total heat exchange in the reactor. More than 94 % of radiant energy lies in the spectral range of 1.99 – 50.0 μm, which just covers the three most important radiation bands of supercritical water. Because both coal particles and supercritical water participate in radiative heat transfer, enhancing radiative heat transfer can effectively improve reaction medium temperature and gasification rate. On average, for every 20 % increase in the proportion of radiative heat transfer in the reactor, fluid medium temperature increases by around 7.1 K, and the gasification reaction rate rises by 9.5 %. These findings would provide valuable guidance for reactor design and optimization in practice.

Influence of Long-Term CaO Storage Conditions on the Calcium Looping Thermochemical Reactivity.

Long-term storage capability is often claimed as one of the distinct advantages of the calcium looping process as a potential thermochemical energy storage system for integration into solar power plants. However, the influence of storage conditions on the looping performance has seldom been evaluated experimentally. The storage conditions must be carefully considered as any potential carbonation at the CaO storage tank would reduce the energy released during the subsequent carbonation, thereby penalizing the round-trip efficiency. From lab-scale to conceptual process engineering, this work considers the effects of storing solids at low temperatures (50-200 °C) in a CO2 atmosphere or at high temperatures (800 °C) in N2. Experimental results show that carbonation at temperatures below 200 °C is limited; thus, the solids could be stored during long times even in CO2. It is also demonstrated at the lab scale that the multicycle performance is not substantially altered by storing the solids at low temperatures (under CO2) or high temperatures (N2 atmosphere). From an overall process perspective, keeping solids at high temperatures leads to easier heat integration, a better plant efficiency (+2-4%), and a significantly higher energy density (+40-62%) than considering low-temperature storage. The smooth difference in the overall plant efficiency with the temperature suggests a proper long-term energy storage performance if adequate energy integration is carried out.

Energy performance assessment of a solar-driven thermochemical cycle device for green hydrogen production

This paper presents a novel dynamic simulation model for assessing the energy performance of solar-driven systems employed in green hydrogen production. The system consists of a parabolic dish collector that focuses solar radiation on two cerium-based thermochemical reactors. The model is based on a transient finite-difference method to simulate the thermal behaviour of the system and it integrates a theoretical analysis of materials and operating principles. Different empirical data were considered for experimentally validating it: a good agreement between experimental and simulated results was obtained for the temperatures calculated inside the thermochemical reactor (R2 = 0.99, MAPE = 6.3%) and the hourly flow rates of hydrogen, oxygen, and carbon monoxide (R2 = 0.96, MAPE = 10%) inside the thermochemical reactor. The model was implemented in a MatLab tool for the system dynamic analysis under different boundary conditions. Subsequently, to explore the capability of this approach, the developed tool was used for analysing the examined device operating in twelve different weather zones. The obtained results comprise heat maps of specific crucial instants and hourly dynamic trends showing redox reaction cycles occurring into the thermochemical reactors. The yearly hydrogen production ranges from 1.19 m3/y to 1.64 m3/y according to the hourly incident solar radiations, outdoor air temperatures and wind speeds. New graphic tools for rapid feasibility studies are presented. The developed tools and the obtained results can be useful to the basic design of this technology and for the multi-objective optimization of its layout and main design/operating parameters.

Enhancing the Potential of Polymer Composites Using Biochar as a Filler: A Review.

This article discusses the scope biochar's uses; biochar is a sustainable organic material, rich in carbon, that can be synthesized from various types of biomass feedstock using thermochemical reactions such as pyrolysis or carbonization. Biochar is an eco-friendly filler material that can enhance polymer composites' mechanical, thermal, and electrical performances. In comparison to three inorganic fillers, namely carbon black, carbon nanotubes (CNT), and carbon filaments, this paper explores the optimal operating conditions for regulating biochar's physical characteristics, including pore size, macro- and microporosity, and mechanical, thermal, and electrical properties. Additionally, this article presents a comparative analysis of biochar yield from various thermochemical processes. Moreover, the review examines how the surface functionality, surface area, and particle size of biochar can influence its mechanical and electrical performance as a filler material in polymer composites at different biochar loads. The study showcases the outstanding properties of biochar and recommends optimal loads that can improve the mechanical, thermal, and electrical properties of polymer composites.

Doped effect of Yb on enhancing resistance to calcium-magnesium-alumina-silicate corrosion of Sm2(Zr0.7Ce0.3)2O7

Four kinds of (Sm1−xYbx)2(Zr0.7Ce0.3)2O7 (x = 0, 0.1, 0.2, 0.3) ceramics with different contents of Yb were prepared by the solid-phase reaction. Their thermochemical reaction behaviors with calcium-magnesium-alumina-silicate (CMAS) at 1300 °C were investigated. Among them, (Sm0.7Yb0.3)2(Zr0.7Ce0.3)2O7 has the best corrosion resistance to CMAS. The increase of Yb content can accelerate the formation rate of apatite, preventing the ceramic layer from erosion of CMAS and improving the strain tolerance of the ceramic. In addition, the CMAS wetting, corrosion process and failure mechanisms were discussed by high-temperature field wetting and transmission electron microscopy.

Application of CoFe2O4-NiO nanoparticle-coated foam-structured material in a high-flux solar thermochemical reactor

Application of CoFe2O4-NiO nanoparticle-coated foam-structured material in a high-flux solar thermochemical reactor

Influence of structural changes on gas transport properties of a cycled CaO/Ca(OH)2 powder bulk for thermochemical energy storage

Thermochemical energy storage using reversible gas-solid reactions has a great potential to evolve into a vital part of a future energy system. A major obstacle for technical application, however, is caused by insufficient gas transport within storage reactors leading to ineffective charging and discharging as well as lower storage densities. Although significant changes in the solid bulk structure are reported throughout the literature, the relevant material property – the bulk permeability – is rarely experimentally studied. In the presented study, the evolution of the gas permeability of a technical grade CaO/Ca(OH)2 powder bulk is studied experimentally. To this end, the pressure drop at ambient conditions is recorded before thermochemical cycling as well as after each dehydration respectively rehydration reaction. The pressure gradient and thereby the permeability is determined based on Darcy's law. The permeability of the fresh Ca(OH)2 bulk after compaction due to the gas flow is 1·10−13 m2. Due to restructuring during thermochemical cycling the permeability increases to 1.6…3.3·10−12 m2 for the cycled Ca(OH)2 bulk and 9.2·10−12 m2 to 2.4·10−11 m2 for the cycled CaO bulk. Further analysis of fresh and cycled samples shows a general increase in particle size and decrease in specific surface area as well as a reduction in reactivity due to agglomeration of the powder. Noticeable is the inhomogeneity of the cycled bulk with powder mixed with larger agglomerates at the top of the bulk and highly porous but seemingly homogeneous solid material at the bottom. Based on the experimental results, gas transport within the agglomerates is identified as a major limiting factor within thermochemical reactors. It is therefore proposed to consider cycled CaO/Ca(OH)2 bulks on a macro- and mesoscale (respectively bulk and agglomerate) simultaneously if transport properties – and their impact on effective reaction dynamics – are relevant.

Investigating the impact of modeling assumptions and closure models on the steady-state prediction of solar-driven methane steam reforming in a porous reactor

In this work, the effect of different modeling assumptions and closure models — frequently considered in the literature of solar thermochemical reactors and closely-related areas — is investigated. The application of different modeling assumptions and closure models may strongly affect the results accuracy and compromise a meaningful comparison across literature works. The following is herein investigated: (i) the role of upstream and downstream fluid regions to the two-phase reactor region; (ii) relevance of species and gas-phase thermal diffusion mechanisms; (iii) reaction heat accounted for in gas- or solid-phase energy balance equations; (iv) local thermal equilibrium (LTE) vs. local thermal non-equilibrium (LTNE) models; (v) model dimension (one-dimensional vs. two-dimensional axisymmetric models); (vi) local volumetric convection heat transfer correlations; and (vii) effective solid thermal conductivity correlations. The relevance of this work extends well beyond the current application (methane steam reforming in a volumetric solar reactor), since similar models and assumptions have also been widely applied for predicting the performance of volumetric solar absorbers and dry reforming solar reactors. The results show that an upstream fluid region should be considered while applying inlet first-type boundary conditions and diffusion transport in the corresponding governing equations to ensure full-conservation and simultaneously to account for developing profiles upstream the reactor inlet section. For the operating conditions considered, species diffusion and gas-phase heat conduction are particularly relevant at the reactor centerline but with a negligible integral effect. A significant difference in the reactor performance is observed while accounting for the reaction heat from surface reactions in the solid- or gas-phase energy balances — for the lowest inlet gas velocity herein considered, the thermochemical efficiency (methane conversion) is approximately equal to 70.8% (76.3%) and 77.3% (84.7%) assigning the reaction heat to the gas- and solid-phase energy balances, respectively. LTE model results are strikingly different from the results obtained with the LTNE model considering the reaction heat accounted for in the gas-phase energy balance but not significantly different from the results computed with the LTNE model with the reaction heat assigned to the solid-phase energy balance. One-dimensional reactor modeling provided with an average concentrated solar heat flux value results in a similar average performance as that given by a two-dimensional model but fails to predict the high temperatures observed at reactor centerline — for the lowest inlet gas velocity, the difference between the maximum solid temperatures predicted by one- and two-dimensional models is about 340K.

ZrO2-MoO3/modified lotus stem biochar catalysts for catalytic aquathermolysis of heavy oil at low-temperature

Aquathermolysis is one of the thermochemical reactions in the heavy oil thermal recovery process. The key issue, i.e., the high temperature required by aquathermolysis, can be reduced by the involvement of catalysts. However, the effective working temperature of catalysts is still above 240 ℃, which needs to be further reduced to enhance energy efficiency. Considering that biochar has a high specific surface area, abundant functional groups, a wide temperature window, and can be easily modified, a series of ZrO2-MoO3-based catalysts loaded on raw or three modified lotus stem biochar were studied to investigate heavy oil catalytic viscosity reduction at low temperatures. Physicochemical properties of catalysts were investigated by a variety of characterization methods. The performance of four kinds of catalysts and the influence of reaction conditions (temperature and time) on aquathermolysis were evaluated. The results showed that silane coupling agent KH570 modified biochar (KH570-MLSB) has a higher specific surface area and more functional groups, which help the loading of active components and the dispersion in heavy oil. ZrO2 can form coordination compounds with S atoms in C-S, which greatly weakens the bond energy of C-S and reduces the activation energy of the aquathermolysis. The coordination bonding energy with S of Mo is weaker than that of Zr. The main role of MoO3 is to inhibit the formation of coke. Therefore, catalyst Ⅳ, which consists of KH570-MLSB, ZrO2, and MoO3, has the best catalytic effect at 200 ℃. In addition, the optimum reaction time of the catalyst is 24 h.

Thermochemically synthesized α‐Al2O3 composite coating with high bonding strength and deuterium permeation resistance

AbstractHydrogen isotope permeation in structural steels can cause severe issues, including steel brittleness, fuel loss, and radioactive pollution in fusion reactors. To tackle this issue, we report a simple synthesis of α‐Al2O3/AlPO4 composite coating by the thermochemical reaction method to serve as an effective barrier hampering hydrogen isotope permeation. This coating was formed at 500°C and composed of α‐Al2O3 and AlPO4 phases. A relatively uniform and compact structure with thickness of ∼35 μm made its corrosion resistance reaching above 3000 times that of the 321 steel substrate. With just one‐side coated, the α‐Al2O3/AlPO4 coating achieved a considerable deuterium permeation reduction factor of 1935 at 450°C, three orders of magnitude higher than 321 steels. What's more, after the deuterium permeation test, no pores or cracks were generated. The excellent bonding between the coating and the substrate was resulted from the formation of CrxPy at their interface induced by Cr diffusion from the substrate. The results obtained from the current study shed new light on seeking reliable and viable ceramic coatings to tackle hydrogen permeation issues.

Applying the solar solid particles as heat carrier to enhance the solar-driven biomass gasification with dynamic operation power generation performance analysis

Solar-driven biomass gasification is a promising technology to improve the utilization efficiency of solar energy and biomass, which also enhances the thermochemical storage and the subsequent stable utilization. Whereas, the intermittence of solar energy deteriorates the stability and continuity of the thermochemical reaction process, which limits the efficient conversion of the reaction. In this regard, this work proposes a new solar-driven biomass gasification technology based on solid particle heat carrier. Different from the direct solar-driven gasification, solid particles are performed as medium to receive the concentrated solar radiation energy and transfer energy to biomass feedstocks. In addition, the combined power generation scenario is adopted to evaluate the thermodynamics and economics of the technology. The integration of solid particle heat storage, the system dispatch and stable operation will be further enhanced. Results show that under the optimal condition, the system maximum thermal and exergy efficiencies are increased by 12.94% and 12.51%, respectively. Considering the system off-design operation, with the evaluated typical periods of four seasons, the averaged power generation efficiency is increased by 5.16%, with the highest efficiency improvement of 9.41% occurring in the typical winter days. With the change of receiver price and biomass price, the maximum decline of levelized cost of electricity reaches to 17.6%, which presents the favorable economic benefits. As a new solar thermochemical technology, this technology exhibits competitive characteristics, significantly improving the utilization efficiency of solar and biomass energy.

UTILIZATION AND REGENERATION OF USED MOTOR OILS WITH THE USE OF MINERAL RAW MATERIALS SOUTH KAZAKHSTAN

The article deals with topical environmental problems of recycling and regeneration of used motor oils. Modern motor oils are alloyed lubricants, as they usually contain several alloying additives that significantly improve the performance properties of the resulting motor oils. During the operation of motor oils, the processes of destruction of motor oils take place as a result of thermochemical reactions, which lead to aging of the oil and a decrease in its quality.