11:45 AM - 12:00 PM
[SVC31-11] Study on relationship between settling velocity of volcanic ash particles and ingestion from air inlet
Keywords:Volcanic ash, Air intake facility, Particle ingestion, gravitational settling velocity
Gas turbines and diesel generators need air for fuel combustion, so they may ingest volcanic ash particles during ash-fall events in volcanic eruptions. These ingested particles may clog the filters in the generator’s air intake system, causing the generator to shut down. Their vulnerability assessment is important, especially for emergency power generators installed at important facilities. Volcanic ash particles are larger and heavier than particulate matters (PMs) and are less likely to follow the airflow due to inertia. Therefore, ingestion of volcanic ash particles at air intake systems may differ from that of PMs, which follow the airflow. To quantify particle ingestions by air intake, ingestion tests were conducted in which settling volcanic ash particles were ingested by an air intake device.
The experimental equipment consists of a chamber, an air intake device, and a particle feeding system [1]. The air intake device uses a suction fan installed downstream of the intake duct to suck air through an inlet installed in the center of the chamber. The particle feeding system, installed at the top of the chamber, uses a feeder with a controllable feeding rate, allowing the test particles to freely settle in the chamber. When suctioning the air in the chamber, the air intake device also ingests the settling particles. The ingested particles are collected by the filter in the air intake device or settle in the intake duct. The mass of the ingested test particles can be quantified by measuring the mass of the filter before and after the test and collecting the particles from the bottom of the duct. In the ingestion test, the ingestion mass ratio, defined as the ratio of the ingestion mass to the feed mass of the test particles, was measured.
The test particles used were volcanic ash particles OS3.5Φ, which were prepared by crushing Osumi pumice and adjusting the size to 63-125 μm using a shaking sieve [2]. The OS3.5Φ sample contains pumiceous and crystalline particles. Since particles with the same gravitational settling velocity are expected to have similar ingestion mass ratios [1], OS3.5Φ should be sieved by gravitational settling velocity using the uniquely designed air elutriation devise. The air elutriation device mixes particles into a vertically upward airflow, and particles with a gravitational settling velocity slower than the airflow velocity move upward with the airflow, while particles with a gravitational settling velocity faster than the airflow velocity settle downward. The test particles also included OS0.17mps, which was prepared by classifying OS3.5Φ using the air elutriation device to a gravitational settling velocity of 0.14-0.20 m/s.
Comparing the results of the ingestion tests of OS3.5Φ and OS0.17mps, the ingestion mass ratio of OS0.17mps tended to be higher than that of OS3.5Φ. Compared with that of OS3.5Φ, the ingestion mass ratio of OS0.17mps was closer to that of 50 μm spherical glass beads with a gravitational settling velocity of 0.17 m/s. The OS3.5Φ has uniform particle size, but it contains pumiceous and crystalline particles of various densities and shapes, and the gravitational settling velocity is not uniform. On the other hand, the OS0.17mps are particles with a gravitational settling velocity adjusted to that of 50μm spherical glass beads. This suggests that the ingestion mass ratio of volcanic ash particles is similar to that of spherical particles with the same gravitational settling velocity. This study reproduced the ingestion of particles with physical properties similar to those of volcanic ash fall undergoing fractionation by gravitational settling velocity rather than particle size during the transport process of volcanic ash in eruptions.
[1] Ozeki et al. Fundamental study on free-settling particles ingested from downward air inlet, JpGU2024 SVC27-08, 2024.
[2] Takeuchi, S. Milling property and texture of porous volcanic rocks, VSJ 2020 Fall Meeting, P55, 2020.
The experimental equipment consists of a chamber, an air intake device, and a particle feeding system [1]. The air intake device uses a suction fan installed downstream of the intake duct to suck air through an inlet installed in the center of the chamber. The particle feeding system, installed at the top of the chamber, uses a feeder with a controllable feeding rate, allowing the test particles to freely settle in the chamber. When suctioning the air in the chamber, the air intake device also ingests the settling particles. The ingested particles are collected by the filter in the air intake device or settle in the intake duct. The mass of the ingested test particles can be quantified by measuring the mass of the filter before and after the test and collecting the particles from the bottom of the duct. In the ingestion test, the ingestion mass ratio, defined as the ratio of the ingestion mass to the feed mass of the test particles, was measured.
The test particles used were volcanic ash particles OS3.5Φ, which were prepared by crushing Osumi pumice and adjusting the size to 63-125 μm using a shaking sieve [2]. The OS3.5Φ sample contains pumiceous and crystalline particles. Since particles with the same gravitational settling velocity are expected to have similar ingestion mass ratios [1], OS3.5Φ should be sieved by gravitational settling velocity using the uniquely designed air elutriation devise. The air elutriation device mixes particles into a vertically upward airflow, and particles with a gravitational settling velocity slower than the airflow velocity move upward with the airflow, while particles with a gravitational settling velocity faster than the airflow velocity settle downward. The test particles also included OS0.17mps, which was prepared by classifying OS3.5Φ using the air elutriation device to a gravitational settling velocity of 0.14-0.20 m/s.
Comparing the results of the ingestion tests of OS3.5Φ and OS0.17mps, the ingestion mass ratio of OS0.17mps tended to be higher than that of OS3.5Φ. Compared with that of OS3.5Φ, the ingestion mass ratio of OS0.17mps was closer to that of 50 μm spherical glass beads with a gravitational settling velocity of 0.17 m/s. The OS3.5Φ has uniform particle size, but it contains pumiceous and crystalline particles of various densities and shapes, and the gravitational settling velocity is not uniform. On the other hand, the OS0.17mps are particles with a gravitational settling velocity adjusted to that of 50μm spherical glass beads. This suggests that the ingestion mass ratio of volcanic ash particles is similar to that of spherical particles with the same gravitational settling velocity. This study reproduced the ingestion of particles with physical properties similar to those of volcanic ash fall undergoing fractionation by gravitational settling velocity rather than particle size during the transport process of volcanic ash in eruptions.
[1] Ozeki et al. Fundamental study on free-settling particles ingested from downward air inlet, JpGU2024 SVC27-08, 2024.
[2] Takeuchi, S. Milling property and texture of porous volcanic rocks, VSJ 2020 Fall Meeting, P55, 2020.