Search Results (23)

Supercritical oxy-fuel combustion, which allows for the high efficiency of power generation with near-zero CO₂ emissions, is considered a promising method to reduce the carbon footprint in the power energy sector. One of the problems in the widespread use of oxy-fuel combustion is a lack of comparative studies on the existing oxy-fuel combustion kinetic mechanisms depending on mixture composition, which complicates the choice of a kinetic mechanism for modeling oxy-fuel combustion. In this paper, a comparative verification of the kinetic mechanisms of GRI-Mech 3.0, UoS sCO₂ 2.0, OXY-NG, and Skeletal was performed using published experimental data on the ignition delay time of methane under conditions of oxy-fuel combustion. A comparative numerical study of the kinetic mechanisms in the wide range of pressures, CO₂ mass fractions in oxidizer (γ), and excess oxidizer ratios (α) by the ignition delay time is also carried out. It was found that the limits of applicability of all of the mechanisms studied are absent when modeling the ignition delay time, the most accurate mechanism to model the IDT of methane in oxy-fuel conditions being UoS sCO₂ 2.0, while the other three mechanisms are overall much inferior to it in terms of accuracy. However, Skeletal and GRI-Mech 3.0 mechanisms can be used to model the IDT during the oxy-fuel combustion of methane under both atmospheric and supercritical conditions, although only in a narrow range of γ. Full article

China has abundant biomass and renewable energy resources suitable for producing green methanol via biomass thermochemical conversion. Given China’s increasing demand for sustainable fuel alternatives and the urgency to reduce carbon emissions, optimizing biomass utilization through gasification is critical. Research has highlighted the potential of integrating biomass gasification with water electrolysis to enhance efficiency in green methanol production, leveraging China’s vast biomass reserves to establish a cleaner energy pathway. Four main biomass gasification technologies—fixed-bed, fluidized-bed, pressurized fluidized-bed, and entrained-flow—have been investigated. Fixed-bed and bubbling fluidized-bed gasification face low gas yield and scaling issues; whereas, circulating fluidized-bed gasification (CFB) offers better gas yield, carbon efficiency, and scalability, though it exhibits high tar and methane in syngas. Pressurized fluidized-bed gasification improves gasification intensity, reaction rate, and equipment footprint, yet stable feedstock delivery under pressure remains challenging. Entrained-flow gasification achieves high carbon conversion and low tar but requires finely crushed biomass, restricted by biomass’ low combustion temperature and fibrous nature. Current industrially promising routes include oxygen-enriched and steam-based CFB gasification with tar cracking, which reduces tar but requires significant energy and investment; oxygen-enriched combustion to produce CO₂ for methanol synthesis, though oxygen in flue gas can poison catalysts; and a new high oxygen equivalence ratio CFB gasification technology proposed here, which lowers tar formation and effectively removes oxygen from syngas, thereby enabling efficient green methanol production. Overcoming feedstock challenges, optimizing operating conditions, and controlling tar and catalyst poisoning remain key hurdles for large-scale commercialization. Full article

Oxygen present in the High Velocity Air-Fuel (HVAF) process can react with the in-flight metallic particles and cause their oxidation. A grown brittle oxide shell on metallic micro-size particles can reduce their deposition efficiency and impair the coating’s final deposited properties/microstructure. In the current study, the oxide growth of MCrAlY particles, where M stands for Nickel (Ni) and Cobalt (Co), during their flight in the HVAF process has been numerically modeled and validated with experimental single-particle depositions. A thorough theoretical oxide layer growth background is also presented. The utilized oxidation development follows the Mott–Cabrera theory for very thin films, which uses the particle surrounding temperature and oxygen partial pressure to track and describe the oxide growth. The obtained results provide a good correlation between the HVAF system design, the operating conditions, and surface oxidation phenomena observed using focus ion beam scanning electron microscope (FIB/SEM) analysis on collected particles. Furthermore, the particle’s degree of oxidation in HVAF is compared to High Velocity Oxy-Fuel (HVOF) to demonstrate the influence of combustion processes on oxidation level. Full article

A flow cell is a critical measurement interface for many optical instruments. However, the flows are often sampled under harsh conditions, such as under high pressure and/or high temperature, in the presence of particles, moisture, vapors with high dew points or corrosive gases. Therefore, obtaining a high-optical-quality flow cell that does not perturb the measurement is a significant challenge. To address this challenge, we proposed a new flow cell that employs a unique laminar coaxial flow field (for the purge and sample flows). A test system was built to conduct particle size distribution (PSD) measurements with no sampling bias using a state-of-the-art analyzer (Malvern Panalytical Insitec). The results revealed that the measurement zone is well defined solely by the sample flow, and the optical windows are well protected by the purge flow, with minimal risk of any depositions from the sample flow. Using this flow cell, the Insitec can successfully measure PSD under high pressure and temperature under moist, corrosive conditions without generating any sampling bias. Importantly, we successfully applied this flow cell for on-line PSD measurement for the flue gas of a 100 kW_th pressurized oxy-coal combustor operating at 15 bara. Full article

Oxy-fuel combustion technology replaces air with a mixture of pure O₂ and recycled flue gas for coal combustion, which leads to difficulties in the waste heat recovery of flue gas in the boiler tail of coal-fired power plants. This paper proposes a new integration scheme for waste heat recovery of flue gas in coal-fired power plants with oxy-fuel combustion CO₂ capture. By introducing an oxygen preheater, a recycled flue gas preheater, and a low-pressure economizer, the waste heat of flue gas is fully recovered to preheat oxygen, recycled flue gas, and feed water, respectively. The proposed scheme simultaneously ensures the safe operation of the recycled fan and improves the thermal performance of the coal-fired power plants. Compared to the air combustion configuration, the boiler’s efficiency and gross power efficiency in the oxy-fuel combustion configuration are increased by 0.42% and 1.29%, respectively. Due to power consumption for the added equipment, the net power efficiency is reduced by 10.41%. A techno-economic analysis shows that the cost of electricity for oxy-fuel combustion in coal-fired power plants has increased from USD 46.45/MWh to USD 80.18/MWh, and the cost of the CO₂ avoided reaches USD 43.24/t CO₂. Full article

Dual-fuel low-temperature combustion is a possible solution for alleviating the tradeoff between oxides of nitrogen and soot emissions in conventional diesel combustion, albeit with poor combustion stability, high carbon monoxide, and unburned hydrocarbon emissions at low engine loads. The present work compares emissions and combustion (heat release and other metrics) of both diesel and poly-oxy methylene dimethyl ether as high-reactivity fuels to ignite natural gas while leveraging spray-targeted reactivity stratification, which involved multiple injections of the high-reactivity fuels. The experiments included six parametric sweeps of: (1) start of first injection, (2) start of second injection, (3) percentage of energy substitution of natural gas, (4) commanded injection duration ratio, (5) rail pressure, and (6) intake pressure. The experiments were performed on a 1.8 L heavy-duty single-cylinder research engine operating at a medium speed of 1339 rev/min. Not-to-exceed limits for the indicated oxides of nitrogen emissions, maximum pressure rise rate, and the coefficient of variation of the indicated mean effective pressure were set to 1 g/kWh, 10 bar/CAD, and 10%, respectively. The indicated emissions decreased and combustion improved significantly for both fueling combinations when the experimental procedure was applied. Full article

In recent years supercritical CO₂ power plants have seen a growing interest in a wide range of applications (e.g., nuclear, waste heat recovery, solar concentrating plants). The Allam Cycle, also known as the Allam-Fetvedt or NET Power cycle, seems to be one of the most interesting direct-fired sCO₂ cycles. It is a semi-closed loop, high-pressure, low-pressure ratio, recuperated, direct-fired with oxy-combustion, trans-critical Brayton cycle. Numerical simulations play a key role in the study of this novel cycle. For this reason, the aim of this review is to offer the reader a wide array of modeling solutions, emphasizing the ones most frequently employed and endeavoring to provide guidance on which choices seem to be deemed most appropriate. Furthermore, the review also focuses on the system’s performance and on the opportunities related to the integration of the Allam cycle with a series of processes, e.g., cold energy storage, LNG regasification, biomass or coal gasification, and ammonia production. Full article

Considering the concerns for emissions reduction in the maritime sector, the present paper evaluates, through modeling and simulation, oxy-fuel combustion in a two-stroke ship engine (2SE) and the best production system configuration to obtain the required oxygen (O₂). An initial model of a ship engine is calibrated with the engine manufacturer’s data and then adapted to work with O₂ as the oxidant to eliminate nitrogen oxide (NO_x) emissions and with exhaust gas recirculation (EGR) to control the in-cylinder combustion temperature. Mixed Ionic–Electronic Conducting (MIEC) membranes produce the necessary O₂ from the ambient air, which is heated up and pressurized by a heat exchanger and turbocharging coupled system to provide the air conditions required for the proper operation of the MIEC. Several layouts of this system are evaluated for the full load engine operating point to find the optimum O₂ production system configuration. Results reveal that the engine operating under oxy-fuel combustion conditions avoids NO_x emissions at the expense of higher brake-specific fuel consumption (BSFC) to obtain the original brake torque, and also expels a stream composed exclusively of CO₂ and H₂O, which facilitates the separation of CO₂ from exhaust gases. Full article

Comparative tests in air and oxy-fuel combustion were conducted in a 30 kW_th circulating fluidized bed (CFB) pilot plant for waste sludge combustion. General combustion characteristics of the CFB, such as pressure profiles, temperatures along the bed, and flue gas composition, were different under the air and oxy-fuel conditions. At the bottom and in the fly ash, alkali and heavy metals had different distributions under the air and oxy-fuel combustion conditions. The particle size distribution in fly ash from air combustion was dominated by coarse particles, over 2.5 μm in size, whereas with oxy-fuel combustion, most particles were submicron in size, approximately 0.1 μm, and a smaller quantity of coarse particles, over 2.5 μm in size, formed than with air combustion. Mass fractions of Al, Ca, and K, below 2.5 μm in size, were found in the ashes from oxy-fuel combustion and in higher quantity than those found in air combustion. Submicron particle formation from Cr, Ni, Cu, and Zn in the fly ash occurred more during oxy-fuel combustion than it did in air combustion. Full article

The article is devoted to the analysis of the flame anchoring mechanism in the test case MASCOTTE C-60 RCM2 on supercritical hydrogen/oxygen combustion at 60 bar, with transcritical (liquid) injection of oxygen. The case is simulated by means of the in-house parallel code HeaRT in the three-dimensional LES framework. The cubic Peng–Robinson equation of state in its improved translated volume formulation is assumed. Diffusive mechanisms and transport properties are accurately modeled. A finite-rate detailed scheme involving the main radicals, already validated for high-pressure ${\mathrm{H}}_2/{\mathrm{O}}_2$ combustion, is adopted. The flow is analysed in terms of temperature, hydrogen and oxygen instantaneous spatial distributions, evidencing the effects of the vortex shedding from the edges of the hydrogen injector and of the separation of the oxygen stream in the divergent section of its tapered injector on the flame anchoring and topology. Combustion conditions are characterised by looking at the equivalence ratio and compressibility factor distributions. Full article

The atmosphere carbon dioxide content grows subsequently due to anthropogenic factors. It may be considerably mitigated by the development of thermal power plants with near zero emissions. A promising way is the transition to the semi-closed oxy-fuel combustion power cycles with carbon dioxide and water vapor mixture as a working fluid. However, their wide implementation requires reduction of the metal consumption for the highly efficient regeneration system. This paper discloses the results of feasibility study for the regeneration system of the prospective oxy-fuel combustion power plant. The effect of operating parameters on the cycle energy efficiency, overall dimensions, and the cost of the regenerator was determined. Underheating increase in the regenerator by 1 °C leads to the net efficiency factor drop of the oxy-fuel combustion power cycle by 0.13% at average and increases fuel costs by 0.28%. Increase of pressure drop in the hot channel by 1% leads to efficiency drop by 0.14%. The optimum set of design and operating parameters of the feed heating system has been determined, which ensures the best technical and economic indicators of electrical power generation: the minimum cumulative costs are achieved when underheating in the regenerator is 20 °C and pressure drop in the hot channel is 4%, under the use of S-shaped fins channels. Full article

This study uses an optimization approach for developing a combustion system in a compression–ignition engine that is able to operate under oxy-fuel conditions, and produces mainly CO${}_2$ and H${}_2$O as exhaust gases. This is achieved because the combustion concept uses pure oxygen as an oxidizer, instead of air, avoiding the presence of nitrogen. The O${}_2$ for the combustion system can be obtained by using a mixed ionic–electronic conducting membrane (MIEC), which separates the oxygen from the air onboard. The optimization method employed maximizes the energy conversion of the system, reducing pollutant emissions (C${}_x$H${}_y$, particulate matter, and carbon monoxides) to levels near zero. The methodology follows a novel approach that couples computational fluid dynamics (CFD) and particle swarm optimization (PSO) algorithms to optimize the complete combustion system in terms of engine performance and pollutant generation. The study involves the evaluation of several inputs that govern the combustion system design in order to fulfill the thermo-mechanical constraints. The parameters analyzed are the piston bowl geometry, fuel injector characteristics, air motion, and engine settings variables. Results evince the relevance of the optimization procedure, achieving very low levels of gaseous pollutants (C${}_x$H${}_y$ and CO) in the optimum configuration. The emissions of CO were reduced by more than 10% while maintaining the maximum in-cylinder pressure within the limit imposed for the engine. However, indicated efficiency levels are compromised if they are compared with an equivalent condition operating under conventional diesel combustion. Full article

The paper is concerned with the problem of the development of high-temperature steam turbine power plants with ultra-supercritical (USC) initial parameters. One of the main disadvantages of the USC power unit’s creation is high price due to the application of expensive heat-resistant materials for boiler, live and reheat steam pipelines in turbines. To solve this problem, the following technical improvements to reduce the application of the heat-resistant materials and equipment metal consumption are proposed: horizontal boiler layout, high temperature steam turbine with a cooling system, oxy-hydrogen combustion chambers, and two-tier low-pressure turbine. The influence of the above-mentioned solutions on the high-temperature steam turbine power plant efficiency was estimated using thermodynamic analysis. The promising equipment design was developed based on the results of numerical and experimental research. The analysis of the proposed solutions’ influence upon the economic parameters of a high-temperature power facility was investigated based on the developed cost analysis model, which included the equipment metal and manufacturing expenses. The introduction of all the mentioned cost reduction methods led to a decrease in the facility’s price by RUB 10.5 billion or 15%. The discounted payback period was reduced from 27.5 to 10 years and the net present value increased by RUB 9.6 billion or 16 times. Full article

China has implemented many green transition policies to reach its carbon peak target, some of which do not consider the actual carbon reduction pressures that localities can afford, thus lowering the living standards of residents and economic growth, which makes the green transition process unsustainable. The Yellow River Basin plays an important role in China’s energy, food, manufacturing, and ecological sectors. Thus, the design of green transition policies in the region needs to be modest and efficient. Based on the data of 100 prefecture-level cities in the Yellow River Basin from 2006 to 2017, this paper uses the K-means clustering to divide the carbon reduction potential of cities into four types. Most cities’ carbon reduction potentials are low or medium, unsuitable for adopting a rapid green transition. Based on the logarithmic mean Divisia index (LMDI) decomposition results and the carbon reduction potential, we designed different carbon-control pathways: Shandong and Henan should focus on increasing investment in green technology, especially oxy-combustion technology; Gansu, Ningxia, and Qinghai could partially offset carbon emissions through land use, land-use change and forestry (LULUCF) activities; Sichuan and Inner Mongolia should increase their energy-use efficiency; Shaanxi and Shanxi could use green finance to complete the upgrading of local industries. The above emission-reduction strategies can be actively pursued in cities with high emission reduction potential and should be implemented with caution in cities with low emission reduction potential. This paper provides a new and cost-effective perspective on carbon emission control in the Yellow River Basin. Full article

Oxy-fuel combustion technology is an effective way to reduce CO₂ emissions. An ionic liquid [emim][Tf₂N] was used to capture the CO₂ in flue gas from oxy-fuel combustion plant. The process of the CO₂ capture was simulated using Aspen Plus. The results show that when the liquid–gas ratio is 1.55, the volume fraction of CO₂ in the exhaust gas is controlled to about 2%. When the desorption pressure is 0.01 MPa, desorption efficiency is 98.2%. Additionally, based on the designability of ionic liquids, a hypothesis on the physical properties of ionic liquids is proposed to evaluate their influence on the absorption process and heat exchanger design. The process evaluation results show that an ionic liquid having a large density, a large thermal conductivity, and a high heat capacity at constant pressure is advantageous. This paper shows that from capture energy consumption and lean circulation, oxy-fuel combustion is a more economical method. Furthermore, it provides a feasible path for the treatment of CO₂ in the waste gas of oxy-fuel combustion. Meanwhile, Aspen simulation helps speed up the application of ionic liquids and oxy-fuel combustion. Process evaluation helps in equipment design and selection. Full article