Heat Effects Of Reactions Research Articles

Reaction heat effect and change characteristics of key groups in coal-oxygen intrinsic reaction path.

The intrinsic reaction of coal with oxygen in the process of low-temperature oxidation is the main reaction path leading to self-heating and spontaneous combustion of coal. Most of the existing studies regard the coal oxidation as an overall reaction, ignoring the multi-path characteristics of coal low-temperature oxidation, and it is difficult to accurately explore the intrinsic reaction characteristics between coal with oxygen. Therefore, the low-temperature oxidation process of coal was studied by using a C80 microcalorimeter and in situ FTIR technology from the macro and micro levels. The "profile subtraction method" was used to study the coal-oxygen intrinsic reaction process, and the reaction heat effect and the change characteristics of key functional groups in the process were analyzed. Furthermore, the gray correlation analysis method was used to study the relevant characteristic parameters in the reaction process and grasp the essential structure-activity relationship. The experimental results show that, compared with the overall reaction process in air atmosphere, the change in the heat release of the coal-oxygen intrinsic reaction path has changed to different degrees, and the change in the slow oxidation stage is the most significant (the heat absorption decreases by 70.1-90.9%). In addition, the characteristic temperature points show different degrees of advance, of which the initial exothermic temperature point is the largest (about 21-46 °C), which directly leads to a significant shortening of the slow oxidation stage (30.1-47.4%). The changes of functional groups in the intrinsic reaction path are more regular. With the increase of temperature, the oxygen-containing functional groups -C=O and the aliphatic hydrocarbon functional groups -CH2- and -CH3 showed a fluctuating trend of increasing and decreasing, respectively. The oxidation heat-contributing functional groups of coal are mainly related to the degree of metamorphism and the functional group reaction characteristics during the reaction. With the deepening of coalification degree, the main heat-contributing functional groups as a whole showed the change rule of oxygen-containing functional groups → aliphatic hydrocarbon functional groups → aromatic hydrocarbon functional groups. In addition, the change of -OH content in the three coal samples has a high correlation with the change of the total heat release of coal.

Design of Reaction Region of Reactive Dividing Wall Column Based on Cross-Wall Heat Transfer

The reactive dividing wall column (RDWC) is a column structure that couples a reactive distillation and dividing wall column. It has become a research hotspot because of its remarkable advantages in energy consumption. Most RDWCs ignore the possibility of cross-wall heat transfer. For the RDWC, the effect of reaction heat is also ignored. In this work, the reaction of methyl acetate with butanol was studied, and Aspen is used to study the effect of the reaction heat and reaction region length on the cross-wall heat transfer. The results show that compared with the RDWC with an adiabatic cross-wall, the RDWC with cross-wall heat transfer can save 3.2% energy. Cross-wall heat transfer could achieve reactants conversion of 99.4%. From the perspective of energy saving maximization, the double reaction region is set. The research results show that the RDWC with cross-wall heat transfer in the double reaction region can save 4.2% energy compared with the cross-wall insulation.

Effect of the phase-transition fluid reaction heat on wellbore temperature in self-propping phase-transition fracturing technology

The key to the success of self-propping phase-transition fracturing (SPF) technology using two immiscible fluids to generate proppants in-situ in a reservoir lies in accurate calculations of temperature distribution. As the reaction heat of phase-transition fluid (PF) significantly affects wellbore temperature, reaction kinetic parameters were fitted by experimental data based on the Arrhenius equation, and the transient temperature model considering the reaction heat is established based on the first law of thermodynamics. This model is discretized by the finite difference method and solved by the successive over-relaxation iteration method. The results show that the reaction heat effect on wellbore temperature cannot be ignored. A temperature value and a phase transition time at the well bottom are the largest in the whole wellbore, so the phase transition ratio at the well bottom is the largest. Moreover, since the PF with incomplete phase transition in a wellbore is easier to enter fractures and prop fracture fronts, it is recommended to inject a pre-pad fracturing fluid before injecting PF to reduce wellbore temperature and prevent premature phase transition in the wellbore. These findings can help reveal the action mechanisms of different injection methods and parameters in a heat transfer process, which is of great significance for the theoretical research and field implementation of SPF technology.

Influences of real-time acid-rock reaction heat on etched fracture dimensions during acid fracturing of carbonate reservoirs and field applications

During acid fracturing, acid-rock reaction heat has a significant influence on temperature profiles in fractures and consequently on etched fracture dimensions, but it is usually neglected or simplified in acid fracturing models. This can lead to misestimating of etched fracture dimensions. A model for calculating real-time acid-rock reaction enthalpy, which is a function of temperature, pressure and volumetric work of carbon dioxide produced by reactions, is coupled into a heat transfer model and a fracture growth model, and its effect on etched fracture dimensions is simulated. True experimental data from SL oilfield in China is used for simulation. The results show that acid-rock reaction heat reduces the effective etched fracture length by around 10%, and the effect of reaction heat on the etched fracture length in limestone is 10%–15% larger than in dolomite. Acid-rock reaction heat makes the etched width profile along a fracture more inhomogeneous. With consideration of acid-rock reaction heat, etched fracture widths are 15%–20% larger near the wellbore and over 20% narrower at fracture tip, and its effects are more intense in limestone than in dolomite. The influences of acid-rock reaction heat on etched fracture dimensions are stronger when the initial formation temperature is lower and when acid of high concentration is used. When the pump rate of acid fracturing is increased, the effect of acid-rock reaction heat on etched fracture dimensions is weakened. The new coupled models were used in carbonate reservoirs in Tarim Basin, China for acid fracturing optimization. A scenario comparison showed that the designed treatment parameters of acid fracturing should be different when acid-rock reaction heat was fully considered. The application of the optimized scenario resulted in at least three folds of production rate increase compared to that before stimulation.

Mitigating catalyst deactivation in selective hydrogenation by enhancing dispersion and utilizing reaction heat effect

AbstractPd catalysts with different particle size were investigated in a strongly exothermic acetylene hydrogenation by changing space velocity. It was found that larger Pd nanoparticles provoked the significant amounts of oligomers and accumulated reaction heat although space velocity had been greatly improved. When Pd particle size was reduced, the number of active sites increased, which contributed to a decrease in heat produced on a single active site, thereby hindered formation of hot spots over catalyst leading to lesser deactivation. Furthermore, by utilizing the features of highly dispersed catalyst without instantaneous heat accumulation, the target acetylene hydrogenation (exothermic) was coupled with acetylene dissociation (endothermic) by sharing reaction heat to construct supported Pd carbide catalysts. Modification of subsurface carbon inhibited the generation of green oil and thus further enhanced selectivity and stability. This work provides an alternative and counter‐intuitive concept where more highly dispersed metal nanoparticles may in fact be more stable.

Effect of the Phase-Transition Fluid Reaction Heat on Wellbore Temperature in Self-Propping Phase-Transition Fracturing Technology

Effect of the Phase-Transition Fluid Reaction Heat on Wellbore Temperature in Self-Propping Phase-Transition Fracturing Technology

In Ukrainian

In this paper, the nature of the chemical activity of pyrolyzed nanostructured carbon materials (PNCM), in particular active carbon (AC), in reactions of electron transfer considered from a single position, reflecting the priority role of paramagnetic centers and edge defunctionaled carbon atoms of carbon microcristallites (CMC) due to pyrolysis of precursors. Clusters in the form of polycyclic aromatic hydrocarbons with open (OES) and closed (CES) electronic shells containing terminal hydrogen atoms (or their vacancies) and different terminal functional groups depending on specific model reactions of radical recombination, combination, replacement and elimination were used to model of nanographenes (NG) and CM. Quantum-chemical calculations of molecular models of NG and CMC and heat effects of model reactions were performed in frames of the density functional theory (DFT) using extended valence-splitted basis 6-31G(d) with full geometry optimization of concrete molecules, ions, radicals and NG models. The energies of boundary orbitals were calculated by means of the restricted Hartry-Fock method for objects with closed (RHF) and open (ROHF) electronic shells. The total energies of small negative ions (HOO-, HO-) and anion-radical О2•‾) were given as the sum of calculated total energies of these compounds and their experimental electron affinities. The estimation of probability of considered chemical transformations was carried out on the base on the well-known Bell-Evans-Polyani principle about the inverse correlation of the thermal effects of reactions and its activation energies. It is shown that the energy gap ΔЕ (energy difference of boundary orbitals levels) in simulated nanographens should depend on a number of factors: the periphery structure of models, its size and shape, the number and nature of various structural defects, electronic states of NG. When considering possible chemical transformations on the AC surface, rectangular models of NG were used, for which the simple classification by type and number of edge structural elements of the carbon lattice was proposed. Quantum chemical calculations of molecular models of NG and CNC and the energy of model reactions in frames of DTF showed that the chemisorption of free radicals (3O2 and N•O), as recombination at free radical centers (FRC), should occur with significant heat effects. Such calculations give reason to believe that FRC play an important role in formation of the functional cover on the periphery of NG in CMC of studied materials. On the base of of cluster models of active carbon with OES new ideas about possible reactions mechanisms of radical-anion О2•‾ formation and decomposition of hydrogen peroxide on the surface of active carbon are offered. Explanation of increased activity of AC reduced by hydrogen in H2O2 decomposition is given. It is shown that these PNCM models, as first of all AC, allow to adequately describe their semiconductor nature and acid-base properties of such materials.

Influence of Composition on Energetic Properties of Copper Oxide – Aluminum Powder Nanothermite Materials Formed by Electrophoretic Deposition

AbstractWe investigated the reactions in composite thermite layers consisting of Al, CuO, and Cu2O nanoparticles formed by electrophoretic deposition on a titanium substrate. The composition determined the reaction propagation rates and heat effects in oxygen and oxygen‐free atmospheres. It was found that a stable self‐propagating exothermic reaction in the aluminum‐copper oxide layer takes place in the range of 50–80 wt.% of Al. The maximum values of the measured heat effects also fell in this range. At the same time, the calculation following the stoichiometry of the reaction shows the optimal range of the Al amount is 10–20 wt.%. To explain this fact, we proposed a model based on calculating the probability of contact between Al and CuO particles depending on the average particle size and their concentration. The model is based on the calculation of solid angles, which means that the exact value of the contact area does not play a decisive role in this case.

Effect of nuclear heat caused by the 6Li(n,α)T reaction on tritium containment performance of tritium production module in High-Temperature Gas-Cooled reactor for fusion reactors

Tritium is required for research and development activities for the deuterium–tritium (DT) fusion reactor and fueling the DEMOnstration Power Station (DEMO). However, tritium is a very rare nuclide and must be produced artificially. Tritium production by loading Li compounds (Li rods) into burnable poison holes of a high-temperature gas-cooled reactor (HTGR) has been proposed (H. Matsuura, et al., Nucl. Eng. Des. 243 (2012) 95–101.). Al2O3 and Zr are used to prevent tritium leaks. Nuclear reaction heat caused by the nuclear reaction (e.g., 6Li(n,α)T reaction) can cause a spatial temperature profile in the Li rods and may change its tritium containment performance, because Al2O3 and Zr performance strongly depend on these temperatures. The effect of nuclear reaction heat by the 6Li(n,α)T reaction on the tritium containment performance of the Li rods was evaluated by simulation. The temperatures of the Li rods for the high-temperature engineering test reactor (HTTR) and gas turbine high-temperature reactor 300 (GTHTR300) increased by 36 K and 46 K, and the leaked tritium decreased by 32% and 37% via nuclear reaction heat, respectively.

Control of Local Electronic Structure of Pd Single Atom Catalyst by Adsorbate Induction.

Aiming at regulating and controlling the localized electronic states while maintaining the metal atoms in the isolation form, an in situ adsorbate induced strategy is proposed at a programmed temperature to activate Zr-based metal-organic framework (MOF) supported single Pd atom catalyst. It is discovered that in situ treatment environments trigger the change of lattice parameters in MOF materials by reaction heat effect, observed by in situ X-ray diffraction, spherical aberration-corrected electron microscope, and X-ray adsorption fine structure (XAFS). The as-obtained electron-deficient Pd single atoms are critical to the high intrinsic activity (turnover frequency of 0.132 s-1 ) and selectivity of 93% with the long-term stability in the semihydrogenation of acetylene, which can be comparable to the state-of-the-art Pd catalysts. This superior catalytic behavior correlates with the reduced C2 H4 desorption energy and the activation barriers for the hydrogenation, confirmed by density functional theory calculation.

Reduction gas obtaining with low content of impurities by two-stage natural gas conversion

Reduction gases are widely used in the metallurgical, chemical and other industries. In this paper, the possibility of higher-quality reduction gas production using a two-stage technology is considered. It is proposed to use air conversion of natural gas with cooling and drying of the obtained products at the first stage. At the second stage, gas mixture is heated, treated in the catalyst bed, quenched and dried. It is established that the temperature of heat treatment of the gas mixture at the second stage should be at least 850–950 °C. This allows to increase the ratio (CO − H2)/CO2 in the resulting reduction gas. The minimum gas treatment temperature at the second stage is calculated depending on the pressure in the system. By overheating the gas before it enters the catalyst bed in the second stage, it is possible to compensate for the heat required for chemical reactions in temperatures above 850 °C, the total thermal effect of chemical reactions is determined. The total heat effect of chemical reactions depending on the temperature of gas heat treatment at different pressure is defined.

Standing window of oblique detonation with pathological behaviour

Standing of an Oblique Detonation Wave (ODW) on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach number. Usually a standing window of ODW is defined as the wedge angle ranged from the ODW detached angle from wedge (upper limit) to the angle that a Chapman-Jouguet (CJ) detonation occurs (lower limit). For pathological detonation cases, however, the CJ detonation cannot be achieved, and thus the lower limit of the standing window of ODW should be revisited. In present study, two types of reactions in hypersonic incoming flow that include the behavior of pathological detonation, that is, the single-step irreversible reaction with mole variation and the two-step irreversible reactions with exothermic process followed by endothermic process, have been used for studying standing behavior of ODW. The steady detonation polar analysis of ODW is carried out for both reaction systems. The results reveal that the reaction with more mole decrement and the reactions with stronger endothermic process show the pathological detonation feature and therefore modify the lower limit of standing window of ODW. Three equivalent parameters are proposed to quantitatively measure the standing window range of ODW from points of view of thermodynamics, Mach number of incoming flow and heat effect of reactions. It is found that the standing window of ODW is determined by the specific heat ratio, the overdrive degree of detonation and the endothermic level of the hypersonic incoming flow, regardless of whether the detonation is pathological or not.

Thermodynamic Characteristics of Protolytic Equilibria of L-Alanayl-L-isoleucine in Aqueous Solutions

Potentiometry and calorimetry are used to study protolytic equilibria in aqueous solutions of L‑alanyl-L-isoleucine. The equilibrium constants and heat effects of the dipeptide dissociation reactions are determined. The standard thermodynamic characteristics of the investigated equilibria are calculated. The obtained results are compared to the corresponding data for related compounds.

Self-propagating synthesis joining of Cf/Al composites and TC4 alloy using AgCu filler with Ni–Al–Zr interlayer

The successful joining of carbon fiber-reinforced aluminum matrix (Cf/Al) composites and TC4 alloy can produce composite structure and meet the demands of lightweight in aerospace field. Up to now, few experimental researches have been reported on the joining of Cf/Al composites and TC4 alloy. In this study, the AgCu foils and Ni–Al–Zr compact were designed for the self-propagating high-temperature synthesis joining of these two materials. Cf/Al composites were joined with a reactive Ti plated on its joining surface. The typical microstructure of TC4/(AgCu/Ni–Al–Zr/AgCu)/Ti/Cf/Al joint was analyzed, and the effects of joining condition on microstructural evolution of the SHS joint were investigated. A thin reaction layer of Ni–Al–Ti intermetallic compounds was formed adjacent to the TC4 alloy. As a result, AgCu foils could reduce the effect of reaction heat on the substrates and improve the joint shear strength. When the thickness of AgCu foils reaches 150 μm, the Ni–Al–Zr interlayer mainly acts as auxiliary heat source. High joining pressure caused the active elements to diffuse into Cf/Al composites and weakened the shear strength of the joint. Finally, the joint shear strength could reach 36.4 MPa when the AgCu foils were 50 μm and the joining pressure was 2 MPa.

ASSESSMENT OF A POSSIBILITY OF QUALITY IMPROVING OF REDUCING GAS BY TWO STAGE NATURAL GAS CONVERSION

The analysis of the method of reducing gas obtaining by natural gas air reforming with cooling and drying of obtained products on the first stage of the process, their heat treatment in the catalyst layer, chilling and drying — on the second stage is made. It is determined that the temperature of a thermal gas treatment at the second stage of the process, shall not be less than 850–950 °C, which allows to increase the ratio (CO + H2)/CO2 in the resulting reducing gas. The values of the minimum temperature of gas processing on the second stage of the process depending on the pressure in the system are calculated. The total heat effect of chemical reactions depending on the temperature of gas heat treatment at different pressure is defined. It is shown the possibility of compensation for the heat expenditure required for the chemical reactions behavior in the temperature region above 850 °C by gas overheating in excess of the required level prior to its entering into catalyst bed on the second stage of the process. Ref. 20, Fig. 3, Tab. 1.

Vibrational nonequilibrium and reaction heat effect in diluted hydrogen-oxygen mixtures behind reflected shock waves at 1000

Vibrationally nonequilibrium model of kinetics in the reacting mixture H2 + O2 + Ar behind the reflected shock wave is formulated as a non-isothermal process occurring adiabatically at a constant volume. The model takes into account the vibrational nonequilibrium for the starting (primary) H2 and O2 molecules, as well as the molecular intermediates HO2, OH, O2(1Δ), and the main reaction product H2O. Calculation results that simulate experimental data on the ignition induction time measurements in the hydrogen oxygen mixtures behind reflected shock waves by the methods of absorption spectroscopy (monitoring the OH(2Π) radical) and emission spectroscopy (monitoring the OH*(2Σ+) radical) at temperatures of 1000 < T < 1300 K and pressures p < 3 atm are compared with experimental data and analyzed. It has been shown that the vibrational nonequilibrium determines the mechanism and rate of the process as a whole. The self-heating effect in diluted reacting mixtures at concentrations of the reacting additive ≤5% is demonstrated and discussed.

Thermal energy storage (TES) capacity of a lab scale magnesium hydro carbonates/silica gel system

In this paper the focus is on the reactive material, reactor design, and heat capacity properties of a TES process. A standardized method for producing the reactive material was developed, for use in a TES reactor vessel. The magnesium hydro carbonate used (Nesquehonite, MgCO3·3H2O) can be produced by a carbon capture and storage by mineralisation process. A composite material for the TES using chemisorption of water is a mixture of MgCO3·3H2O and silica gel. Several heat effects were tested simultaneously with a set up for 40–70 g composite material using temperature and relative humidity sensors to monitor the hydration reaction and its conditions. Operating temperatures and humidity were measured inside the reactor, in a set up design that matches the parameters of a novel technical concept, while also the maximum reaction heat effect using the composite material was measured. A thermal storage capacity of 0.41 MJ/kg using 70 g composite material could be measured, while using 3 g sample a hydration/chemisorption effect of 0.71 MJ/kg was obtained. Heating system containing a heat pump would use the TES as an extra heat source during colder periods which implies improved efficiency and COP.

Heat transfer analysis of a high-power and large-capacity thermal battery and investigation of effective thermal model

We perform heat transfer analysis of a thermal battery module for a high-power and large-capacity thermal battery system based on a detailed thermal model as well as an effective thermal model. Firstly, the transient thermal behavior of a small scale thermal battery module consisting of 13 stacks of unit cells is investigated by the detailed thermal model that considers every components. We show that the net effect of Joule heating (exothermic) and chemical reaction heat (endothermic) occurring in the unit cell result in different degree of cooling down the thermal battery depending on the operating condition. It is also found that anisotropic heat conduction due to the stacked geometry of the unit cell causes temperature non-uniformity within the thermal battery module. Secondly, we also develop an effective thermal model based on the properly averaged thermophysical properties of constituent materials of unit cells as well as the homogenized heat sources. The effective thermal model is validated by comparing it with the detailed thermal model for the small scale thermal battery module consisting of 13 stacks of unit cells, and it is further extended to the large scale thermal battery module consisting of 54 stacks of unit cells.

Investigation of metal oxides, mixed oxides, perovskites and alkaline earth carbonates/hydroxides as suitable candidate materials for high-temperature thermochemical energy storage using reversible solid-gas reactions

Thermochemical storage of solar heat involves the heat effects of reversible chemical reactions and can be coupled with a solar thermal power plant for continuous electricity generation. A comprehensive study of chemical materials for thermochemical heat storage based on reversible redox reactions was conducted. The evaluation of the selected systems was based on their suitable transition temperatures, chemical conversion rates, reversibility, energy storage density as well as general criteria such as toxicity and cost, and resulted in the selection of metal oxides (based on Co and Mn), perovskites and carbonates/hydroxides (of Ca, Sr, Ba).For metal oxides processed in air, Co3O4/CoO was cycled as powder bed and porous foam without reactivity loss, whereas Mn2O3/Mn3O4 showed poor reversibility, which can be enhanced via the synthesis of porous microstructure. The potential improvement of their performance was further studied using transition metal addition. The addition of Fe, Cu or Mn to Co3O4/CoO was found to adversely decrease the redox activity and energy storage capacity. In contrast, the reaction rate, oxygen exchange capacity, reversibility and stability of Mn2O3/Mn3O4 were significantly enhanced with added Fe, Co, or Cu amounts above ∼15, 40 and 30 mol% respectively, while the energy storage capacity was improved accordingly.Perovskites represent another attractive class of thermally-stable redox materials (e.g., energy storage density above 200 kJ/kg for Ca0.5Sr0.5MnO3), but the continuous lattice oxygen transfer may be a barrier for the recovery of the absorbed energy, thus requiring pressure-swing operation with inert gas utilization. Finally, carbonates and hydroxides were identified as promising candidates chiefly because they exhibit the highest energy storage capacities among the considered materials, but they require closed-loop operation. Among these systems, both SrCO3/SrO and Sr(OH)2/SrO stabilized with MgO as well as Ca(OH)2/CaO showed remarkable cycling stability and energy storage densities.

A process model for underground coal gasification – Part-III: Parametric studies and UCG process performance

Underground gas gasification (UCG) is a clean coal technology which involves in-situ gasification of deep-seated underground coal. The process can be divided in two phases based on state of coal seam and direction of cavity growth. In phase-I, cavity grows mainly in vertical direction while in phase-II it grows in horizontal direction. The in-house simulator developed for both the phases of UCG has been reported earlier Samdani et al. (2016a,b). It incorporates reaction kinetics, flow patterns, spalling, heat and mass transfer effects. In this work, we take further insight and perform parametric studies to examine the effects of different operating conditions, coal properties and design parameters on key performance indicators i.e. exit gas quality, energy generation rates etc. The investigation revealed that the exit gas quality and rate of coal consumption are strong functions of spalling rates and kinetics of reactions; the coal having very low spalling tendency or less reactivity may not be favorable for the UCG process. An important parameter called critical spalling rate has emerged through this analysis. It is the property of given coal above which UCG is sustainable. In addition, model performance is also sensitive to inlet gas temperature, pressure and composition. Optimum performance of UCG is obtained at a steam to oxygen ratio of 2.5 and at the highest possible inlet gas temperature, operating pressure, and oxygen content in the feed. Among the design parameters, the length of outflow channel is very important as it strongly affects both the exit gas calorific value and its fluctuations with time. The predicted effects of different parameters are in accord with the observations during lab-scale UCG experiments and different field trials. This study demonstrates the importance of a process model to determine the best conditions for UCG process and to evaluate feasibility of the process for a coal seam under consideration.