The influence of Stefan flow on the flow and heat-transfer characteristics of spherical-particle pair in supercritical water

Self Cite

Supercritical water gasification is an efficient and clean way of energy conversion. The research on different scales, such as the system, reactor, and particle, has different temporal and spatial significance. A study on particle−particle and particle− fluid−particle interaction on the particle scale has a fundamental guiding value for revealing gasification performance on the reactor scale. Reactive particles such as coal are pyrolyzed and gasified in a high-temperature and high-pressure reactor to form Stefan flow, which affects the mass, momentum, and energy transfer between particles and supercritical water. In this paper, a particle-resolved direct numerical simulation study of a reactive particle layer in supercritical water is carried out to investigate the effect of different particle layer solid holdups and Stefan flow intensities and distributions on the flow and heat transfer process between the particle layer and supercritical water. This work analyzes the pressure and friction drag coefficients to which the particles are subjected and specifies the flow, velocity, and temperature distribution inside and around the particle layer. The results show that the drag coefficient and Nusselt number of particles in the particle layer decrease gradually along the flow direction, and the presence of particle Stefan flow further reduces the drag force and Nusselt number of particles. With the increasing solid holdup of the particle layer, the particle−fluid−particle interaction becomes more intense, and the effect of Stefan flow cannot be negligible.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Direct Numerical Simulation of Fluid Flow and Heat Transfer of a Reactive Particle Layer with Stefan Flow in Supercritical Water

Wang

Jin

2023

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“…Potential impacts of irreversible plastic pollution include changes in carbon and nutrient cycling; habitat changes in soil, sediment, and aquatic ecosystems; concurrent biological impacts on endangered or critical species; ecotoxicity; and associated societal impacts . In response to this dilemma, plastic degradation technology has also been widely studied. − …”

Section: Introductionmentioning

confidence: 99%

Study on Carbon Fixation and Gasification of Polypropylene and Polycarbonate in a CO₂ Environment

Zhao

Zhu

Bai

et al. 2022

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The ability of plastics to consume CO2 captured in industries while being pyrolyzed is extremely valuable. In this paper, the gasification and carbon fixation of polypropylene (PP) and polycarbonate (PC) during pyrolysis in a CO2 atmosphere at different temperatures and reaction times were investigated. At the same time, other plastics are pyrolyzed in the CO2 environment to compare the carbon fixation capacity of the plastics, including polylactic acid plastic and polystyrene plastic. The results showed that after a 30-min reaction time at 750 °C, the carbon conversion efficiency (CE) of PP plastic and PC plastic reaches 45.1% and 32%, respectively. When the temperature is 600 °C, PP plastic can fix carbon, and the longer the reaction time, the greater the effect of temperature. Furthermore, when PC plastic and PP plastic are copyrolyzed, the presence of PC plastic will reduce the carbon fixation ability of PP plastic, and it was found that only plastic polymers with very little oxygen content were able to fix CO2 in the pyrolysis process. Pyrolysis of PP plastic and PC plastic also produces fused-ring aromatic compounds such as naphthalene and anthracene and carbon microspheres.

“…First, organics could be dissolved in SCW easily and form a homogeneous system, reducing phase resistance. Second, this technology is efficient and clean, without NO x and SO x emission because the N, S element is converted into inorganic salt, which reduced the emission of pollutants, and CO 2 could be captured easily. , Therefore, promoting the industrialization of this technology earns much attention now …”

Section: Introductionmentioning

confidence: 99%

“…Second, this technology is efficient and clean, without NOx and SOx emission because the N, S element is converted into inorganic salt, which reduced the emission of pollutants, and CO 2 could be captured easily. 7,8 Therefore, promoting the industrialization of this technology earns much attention now. 9 The reactor surely becomes the research focus because it is the most important component in the gasification system.…”

Section: Introductionmentioning

confidence: 99%

Development of a Partitioning Kinetic Model of Biomass Gasification in Supercritical Water with a Fluidized Bed Reactor

Wang

Jin

2022

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Biomass supercritical water gasification technology is considered an effective way to realize the utilization of biomass, and further development of this technology depends on an accurate kinetic model. In this work, the reactor was distributed into a nozzle affected zone, a dense phase zone, and a freeboard zone according to the characteristic of the physical and chemical field, and a reaction kinetic model suitable for each zone was developed, which could be used for dynamic and scale-up studying of the reactor. First, three groups of gasification experiments (feedstock and biochar with low and high concentrations) were conducted to obtain the gas yield for calculation of the kinetic parameter, and obtain the evolution of the specific area of biochar for the calculation of the porous structure constant ψ. Then, detailed reaction pathways for biomass and biochar were proposed and a random pore kinetic model taking specific surface area into account was developed based on the first order of each reactant.