Hydrodynamics of High-Density Downer Reactors Using a Novel Solids Feeder
Bibliographic record
Abstract
Downer reactors have many advantages over risers for reactions requiring very short residence time. However, its application for reactions where a high solid/gas ratio is required has been restricted by the low solids holdup in the fully developed region (typically less than one percent). In this paper, we present the performance of a 0.078 m diameter and 3.2 m long high-density downer reactor equipped with a recently developed novel solids feeding system.Experiments were carried out using fluid coke particles of particle density 1600 kg/m3 and mean diameter 133 mm, with solids fluxes up to 1400 kg/m2s and superficial gas velocities ranging from 0 to 6 m/s. The downer was operated under batch mode, with solids fed from a solids feeder installed inside a fluidized bed at the top of the downer and the bottom end of the downer connected to a receiving hopper. The solids flux was controlled by a butterfly valve installed 0.4 m below the downer entrance. Air was injected into the downer through four 45-degree-angled nozzles located right below the butterfly valve. Solids were lifted up from the bottom receiving-hopper to the upper fluidized bed through an external riser after each run.The cross-sectional average solids hold-up calculated from the integration of local measurements obtained from a capacitance probe was found to be a function of both the solids flux and superficial gas velocity. The solids hold-up increased with increasing solids flux at a given superficial gas velocity, but decreased with increasing gas velocity at a fixed solids flux. A cross-sectional average solids holdup of 16.5% was achieved at an axial position of 3.0 m below the air injection point under the operating condition of Gs=1400 kg/m2s and Ug=2.0 m/s. The shape of radial solids distribution varied not only with the superficial gas velocity but also with the solids flux in high-density downers. The radial solids distribution became more uniform under higher solids fluxes and lower gas velocities. The dense ring at the near wall region disappeared under the high-flux operating condition (Gs=1400 kg/m2s, Ug=2.0 m/s). The radial solids holdup profiles became less uniform, denser near the wall and more dilute and non-uniformly distributed in the central region, as the gas velocity increased from 3.0 to 6.0 m/s at a fixed solids flux of about 400 kg/m2s, which is significantly different from flow patterns reported in the literature under lower solids flux conditions.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".