Reverse Combustion Research Articles

ТЕПЛОФИЗИЧЕСКАЯ МОДЕЛЬ И РЕЗУЛЬТАТЫ ЭКСПЕРИМЕНТАЛЬНОГО ИССЛЕДОВАНИЯ ГАЗИФИКАЦИИ ДРЕВЕСНЫХ И РАСТИТЕЛЬНЫХ ОТХОДОВ

The article compares the calculation results using the developed thermophysical composition model for the study of thermal gasification of wood and plant waste – renewable natural energy resources in a gas generator with the reverse combustion process and forced steam-air blast, which allows to achieve minimal formation of a by-product – resin. Based on the thermophysical model, the optimal consumption of solid fuel – wood and plant waste and oxidizer – atmospheric air is determined. The work can be used by technical engineers at enterprises in Russia and abroad for the environmentally friendly disposal of wood and plant waste in autonomous energy technology installations with combustion gas generators to generate thermal and electrical energy for the consumer. In particular, large volumes of wood and plant waste accumulate at wood processing and agricultural enterprises in the Tyumen region, which are an additional cheap source of energy.

Reverse combustion propagation in an oxygen-limited and -enriched N2/O2 flow for a bed packed with rice husk

Propagation characteristics of reverse combustion significantly impact the conversion of solid fuels in packed beds, especially under variable reaction atmosphere conditions. In this study, the propagation of reverse combustion was experimentally studied in an oxygen-limited and -enriched O2/N2 flow with an oxygen concentration range of 21–100 % for a bed packed with rice husk. The temperature profile measured by thermocouples along the bed height was processed to appreciate the driving mechanism of combustion front, as well as the reaction structure inside the bed. Besides, the contribution of volatiles gas-phase oxidation and char surface oxidation to reverse combustion was also evaluated. Results show that compared to the air case, an oxygen-enriched condition broadens the operating range of oxygen flow rate for the oxygen-limited reverse combustion. Under high oxygen concentration conditions, the low-temperature oxidation of rice husk inside the reaction front becomes enhanced. Such chemical reaction effect widens the whole reaction front thickness and thereby reduces the oxidation intensity in local regions, resulting in a faster ignition rate and a lower temperature for combustion front. It is found that this process is dominated by the gas-phase oxidation of volatiles, of which oxygen consumed is above 60 % of the supplied. As oxygen concentration increases, the gas-phase oxidation of volatiles becomes further enhanced. Correspondingly, the oxidation ratio of char is gradually approaching a limit, about 12 %, especially at the oxygen concentration above 50 %. These findings will facilitate a better fundamental understanding of driving mechanism of this special combustion process and thereby provide an important theoretical basis for efficient thermal conversion of solid fuels.

The Lean-Burn Limit Extending Experiment on Gasoline Engine with Dual Injection Strategy and High Power Ignition System

In the context of the energy crisis and global warming, improving thermal efficiency is the most important issue in research on gasoline engines, and lean mixture combustion strategy is becoming the most promising method. Thus, a high compression ratio, a high-power interval ignition system, and a stratified combustion scheme achieved via dual injection were novelly adopted in a single cylinder gasoline engine in this study. The results show that the lean combustion limit could be literally extended and improved thermal efficiency was observed under the ultra-lean condition. Meanwhile, reverse combustion performance trends were observed by altering the second injection proportion from 30% to 45% under the lean condition (λ = 1.6) and ultra-lean condition (λ = 1.9). This was related to a combustion velocity change caused by great concentration gradient at the middle and end combustion stage. Finally, according to research on the effects of altering the timing of the second injection, it is clear that the dual injection strategy is an ideal method for realizing operation under the lean condition (λ = 1.6). But for the operation under the ultra-lean condition (λ = 1.9), more injection times and suitable air flow organization are needed to enhance the robustness of mixture distribution.

Design of intelligent compound pyrolysis unit for hazardous waste of biomass backburning based on computer simulation

This system generates combustible gas and ignites it by generating combustible gas through the internal heating pyrolysis combustion of biomass fuel in the reverse combustion furnace and outside the pyrolysis furnace, which promotes the pyrolysis of biomass fuel while heating the pyrolysis furnace, pyrolysis of hazardous waste in the pyrolysis furnace, and realizes the recycling of heat energy.

“Reverse combustion” of carbon dioxide in water: The influence of reaction conditions

The synthesis of value-added organic products from the hydrothermal conversion of CO2 and H2O has been demonstrated, revealing the impact that reaction conditions have on the product distribution and yield. CO2 has the potential to become a valuable feedstock for the chemicals sector, in part displacing fossil resources and improving the economics of carbon capture. Herein the conversion of CO2 with H2O, in the absence of gas-phase H2, to methanol and other products is shown to occur under sub-critical water conditions in the presence of iron as a reductant and catalyst: this process can be considered as a form of “reverse combustion”. The influence of reaction temperature between 200–350°C and CO2:O2 mole ratio from 9 to 119 (in addition to pure 100% CO2) have been investigated in the presence of Fe powder. The influence of reaction time has also been investigated, employing Fe3O4 as a catalyst. Product analysis is conducted by GC-MS and MS for liquid- and gas-phase products respectively, while SEM and XRD are employed to analyse morphological changes in the catalyst and TPO investigates any coke deposited during reaction. Methanol is the major product formed at all conditions investigated, with a maximum concentration of 8 mmol L−1 after 12 h of reaction, or after 4 h in the presence of oxygen. Acetone and ethanol are also formed, although in smaller quantities than methanol, with larger-chained species also present. An inverse relationship is observed between acetone and ethanol concentrations. Based on the analysis of the reaction data it is hypothesized that ethanol and acetone may be competitively produced in one reaction pathway, while methanol is produced in an independent, parallel, pathway. The observation of acetaldehyde in the gas-phase at all studied conditions suggests that acetone may be produced from the dehydrogenation of ethanol via an acetaldehyde intermediate; catalyzed by zero-valent iron sites. Morphological characterization indicates that the catalysts are stable under the reaction conditions. These studies facilitate the development of improved catalysts and processes for the hydrothermal conversion of CO2, allowing further development of this promising sustainable process.

Experimental Investigations of Forward and Reverse Combustion for Increasing Oil Recovery of a Real Oil Field

The work presented herein is devoted to a unique set of forward and reverse combustion tube (CT) experiments to access the suitability and potential of the in situ combustion (ISC) method for the light oil carbonate reservoir. One forward and one reverse combustion tube tests were carried out using the high-pressure combustion tube (HPCT) experimental setup. However, during reverse combustion, the front moved in the opposite direction to the airflow. The results obtained from experiments such as fuel/air requirements, H/C ratio, and recovery efficiency are crucial for further validation of the numerical model. A quantitative assessment of the potential for the combustion was carried out. The oil recovery of forward combustion was as high as 91.4% of the initial oil in place, while that for the reverse combustion test demonstrated a 43% recovery. In the given conditions, forward combustion demonstrated significantly higher efficiency. However, the stabilized combustion front propagation and produced gases of reverse combustion prove its possible applicability. Currently, there is a limited amount of available studies on reverse combustion and a lack of publications within the last decades despite advances in technologies. However, reverse combustion might have advantages over forward combustion for heavy oil reservoirs with lower permeability or might serve as a reservoir preheating technique. These experiments give the opportunity to build and validate the numerical models of forward and reverse combustion conducted at reservoir conditions and test their field application using different scenarios.

How to Burn? Straight vs Horizontal vs Suspended

Burning is an inevitable process that happens in nature and has a massive impact on life. Technically, burning or combustion emphasizes on the reaction process that consumes oxidizer and fuel to deliver heat and burnt products. Based on the direction of reaction propagation and fuel orientation, burning or combustion is classified in to forward or reverse combustion. Forward combustion is a process which comprises of movement of air and the propagation of ignition zone in the same direction while in reverse combustion, air moves opposite to the direction of the propagation of the ignition zone. Forward combustion escalates rapidly in solid fuels when compared to reverse combustion. The conductivity of the burning solid fuel, convection due to the atmospheric air around and buoyancy effects which takes place due to the difference in air densities plays a major role in the forward combustion process. In this work, thin uniform cross-sectioned solid materials such as matchsticks, candles and incense sticks have been considered as fuel to investigate forward flaming and smoldering. The experiments were carried out in ambient atmospheric conditions. The results based on visualizations suggest that the orientation of the fuel has a greater impact on burning rates and provides us the information on how to burn it in a beneficial way.

A Multi-Scale Approach for Reverse Engineering Chemical Looping Combustion

A Multi-Scale Approach for Reverse Engineering Chemical Looping Combustion

Effects of High-temperature Char Layer and Pyrolysis Gas on NOx Reduction in a Typical Decoupling Combustion Coal-fired Stove

The suppression of nitrogen oxides (NOx) is the key to reducing pollutant emission of a domestic coal-fired stove due to the limitation of technology condition and economic cost. The decoupling combustion (DC) technology invented by Institute of Process Engineering (IPE), Chinese Academy of Sciences (CAS) is characterized by that a traditional stove is separated into a pyrolysis and a combustion chamber as well as a bottom passage between them. In this study, the combustion of briquette from bituminous coal in different operation modes in a typical decoupling stove is tested and simulated to validate the advantage of DC technology over so-called reverse combustion. The smokeless and high-efficiency combustion of bituminous briquette with low emissions of NOx and CO can be implemented by utilizing low NOx combustion under low temperature and reduction atmosphere in the pyrolysis chamber as well as after-combustion of char and pyrolysis gas under high temperature and oxidation atmosphere in the combustion chamber. The effects of the main reducing components in pyrolysis gas as well as char on NOx reduction were numerically investigated in this study, which shows that the reducing ability increases gradually from CH4, CO to char, but the combined reducing ability of them cannot be determined by a simple addition.

Electrochemical Investigation of CO2 Conversion Utilizing Nanoporous Polystyrene-Polyvinylpyridine Catalyst

The threat of climate change proves to be one of mankind’s most daunting challenges. Carbon dioxide emissions are believed to be a leading contributor to climate change. The development of nontoxic and abundant catalysts for the reduction of CO2 is critical in enabling this much needed technology. A method of reverse combustion would be prove to be advantageous in mitigating climate change and providing for a carbon neutral fuel source. Pyridine has shown to be electrocatalytically active at reducing carbon dioxide at low overpotentials to hydrocarbons.The development of nanoporous polymer thin films have exhibited many useful properties that have yet to be exploited. Taking advantage of the microphase separation phenomenon of poly(styrene)poly(4vinylpyridine), PSP4VP, block copolymers allows for pyridine moieties to assemble onto the cylindrical interior of these nanoporous surfaces. These moieties we've shown to be both electrocatalytically active in conjunction with conductive cocatalyst via a radical mechanism.

Modelling of reverse combustion linking in underground coal gasification

Reverse combustion linking (RCL) is a viable and effective linking method for underground coal gasification (UCG). A modelling tool was employed here to explore the theory of reverse combustion in porous media. Grid refinement was also applied to capture accurately the fire-front propagation. Simulation results indicated that RCL features a low-temperature process with strong coupling of mass and heat transfer and chemical reaction kinetics so that caution must be taken for successful implementation; for example, water removal by air flooding is imperative. In addition, at a higher injection rate and pressure, reaction kinetics and heat transfer become limiting factors for front propagation. Therefore, except for an expanding diameter linkage, an increase in the injection rate and pressure contribute essentially little to the linking speed in the parameter range of interest. The results also showed that the hot linkage and abundance of char in place after RCL are of benefit to UCG. In the end, favorable factors were also studied and identified for securing a successful RCL for UCG.

CO2 Conversion Via Nanoporous PS-PVP Block Copolymer: Revisiting the Pyridyl Radical

The threat of climate change proves to be one of mankind’s most daunting challenges. Carbon dioxide emissions are believed to be a leading contributor to climate change. The development of nontoxic and abundant catalysts for the reduction of CO2 is critical in enabling this much needed technology. A method of reverse combustion would be prove to be advantageous in mitigating climate change and providing for a carbon neutral fuel source. Pyridine has shown to be electrocatalytically active at reducing carbon dioxide at low overpotentials to hydrocarbons.The development of nanoporous polymer thin films have exhibited many useful properties that have yet to be exploited. Taking advantage of the microphase separation phenomenon of poly(styrene)-poly(4-vinylpyridine), PS-P4VP, block copolymers allows for pyridine moieties to assemble onto the cylindrical interior of these nanoporous surfaces. These moieties we've shown to be both electrocatalytically active in conjunction with conductive co-catalyst via a radical mechanism.

Converting carbon dioxide into alkanes via alkane reverse combustion reaction

Converting carbon dioxide into alkanes via alkane reverse combustion reaction

Forward and reverse combustion gasification of coal with production of high-quality syngas in a simulated pilot system for in situ gasification

This research focused on the feasibility and stability of applying the forward and reverse combustion approach to the in situ gasification of lignite and bituminous coal with oxygen or oxygen–steam mixtures as gasification agents, especially reverse combustion gasification. A high-quality syngas (H2 and CO) could be obtained using the reverse combustion gasification technique combined with forward combustion gasification in a pilot system for in situ gasification. The gasification time was extended more than 25% using the reverse combustion approach. The controlling conditions for reverse combustion gasification were obtained by comparing and analyzing experimental data. The results show the relationship between the inject gas flow within certain limits and velocity of the gasification flame was linear during reverse combustion. The underground conditions of the coal seam and strata were simulated in a pilot-scale underground gasifier during experiments. The combustion gasification of coal was carried out experimentally for over 5days. The average effective content (H2 and CO) of syngas was in the range of 60–70%, meeting the requirement of synthesis gas. The optimal ranges of gasifying lignite and bituminous coal were found to be 1.5–2.0 and 1.3–1.75, respectively. The product gas flow was proportional to oxygen blast. These are expected to provide useful guidance on practical underground coal gasification operations and to give experimental evidence in support of theory.

Experimental forward and reverse in situ combustion gasification of lignite with production of hydrogen-rich syngas

AbstractThis research focused on the feasibility of applying the forward and reverse combustion approach to the in situ gasification of lignite with the production of hydrogen-rich syngas (H2 and CO). The so-called forward combustion gasification (FCG) and reverse combustion gasification (RCG) approach in which oxygen and steam are simultaneously fed to the simulated system of underground coal gasification (UCG) was studied. A simulated system of UCG was designed and established. The underground conditions of the coal seam and strata were simulated in the system. The combustion gasification of lignite has been carried out experimentally for almost 6.5 days. The average effective content (H2 + CO) of syngas during the FCG phase was 62.31 % and the maximum content was 70.92 %. For the RCG phase the corresponding figures are 61.33 % and 67.91 %. Thus, the feasibility of using RCG way for UCG has been demonstrated. The temperature profiles have been provided by using of 85 thermocouples during the model experiment, which portrayed the several nephograms of thermal data in the gasifier were of significance for the prospective gasification processes.

Pattern formation in reverse smouldering combustion: a homogenisation approach

The development of fingering char patterns on the surface of porous thin materials has been investigated in the framework of reverse combustion. This macroscopic characteristic feature of combustible media has also been studied experimentally and through the use of phenomenological models. However, not much attention has been given to the behaviour of the emerging patterns based on characteristic material properties. Starting from a microscopic description of the combustion process, macroscopic models of reverse combustion that are derived by the application of the homogenisation technique are presented. Using proper scaling by means of a small scale parameter ϵ, the results of the formal asymptotic procedure are justified by qualitative multiscale numerical simulations at the microscopic and macroscopic levels. We consider two equilibrium models that are based on effective conductivity contrasts, in a simple adiabatic situation, to investigate the formation of unstable fingering patterns on the surface of a charred material. The behaviour of the emerging patterns is analysed using primarily the Péclet and Lewis numbers as control parameters.

Efficient Combustion: A Process Synthesis Approach to Improve the Efficiency of Coal-Fired Power Stations

Much of our energy reserves are locked in the chemical potential of chemicals such as fossil fuels. The majority of CO2 emissions caused by human activities come from the combustion of these fuels. Typically, the fuel is burned with oxygen (air), and heat is released. This heat is then used to drive power cycles to produce, for example, electricity in a power plant or motion in the motor car engine. Often, the performance of these processes is assessed in term of thermal efficiency (ηth), which considers how much of the energy released in the combustion process is turned into work. This is not a good representation of how efficient the process is, however, as an idealized Carnot engine, which takes heat from a heat source at a temperature TH and rejects heat to a heat sink at the reference temperature T0 = 298.15 K, is reversible and thus takes all of the work potential (exergy) of heat and converts this to work. Thus, the Carnot engine might have only 40% efficiency in terms of converting heat to work (ηth), but because it is fully reversible, it generates no entropy, and therefore, it is 100% efficient in terms of recovering the work potential of heat. However, there is a much more fundamental efficiency that should be considered, namely, how much of the chemical potential of the fuel is turned into work. When combustion processes are considered in this way, it becomes clear that some of the major inefficiencies are in the chemical transformations that produce heat, rather than in the power cycles that convert heat to work. A very important question remains: Is it possible to do these transformations more efficiently and thereby conserve the work potential or chemical potential in fuel? This article shows, from a fundamental thermodynamic analysis, that it is not possible to combust carbon-based materials efficiently, that is, that the process of combustion of carbon-based materials is irreversible and that a considerable amount of the chemical potential of the fuel is lost during the combustion process. However, other substances or chemistries are explored in this work, and it is shown that some of these have the potential for more reversible combustion. These options are explored, and their potential implementation is examined by considering a coal-based power plant as an example. In particular, it is shown that CO2 emissions could be significantly reduced by using different chemical pathways to do the combustion and by combining power and chemical production.

Reverse Combustion: The Efficient Electrochemical Conversion of Carbon Dioxide and Water to Organic Fuels Using an Aromatic Amine Catalyst

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Hydrogen production in a reversible flow filtration combustion reactor

The noncatalytic process of syngas production by means of partial oxidation of methane by air oxygen in a reversible flow filtration combustion reactor has been investigated experimentally. We have investigated the influence of the equivalent ratio and the specific mass flow of the fuel mixture on the composition of conversion products and the maximum temperature in the reaction zone. The optimal conditions for the process providing the most effective conversion of methane to syngas have been established. The concentration of hydrogen is maximal for the equivalent ratio γ = 2.8 and the specific flow rate g = 1.8 kg / (m2⋅s).

Exergetic Destruction Effects of Operating Conditions on the Turbojet Engine Components

The minimization of exergy destruction brings the design as closely as permissible to the theoretical limit. This study presents exergy destruction analysis of a turbojet engine for different flight Mach number and altitudes. Turbojet engine being considered consists of an inlet, a centrifugal compressor, reverse flow combustion chamber, axial-flow turbine and exhaust nozzle. The flight Mach number and altitude are examined on the exergetic destructions of compressor, combustion chamber, turbine and exhaust nozzle. The results of component-based destruction analysis are given as three dimensional exergetic-destruction response surface plots related to altitude and flight Mach number.