Abstract

Many sophisticated instruments are available for obtaining detailed information about aerosol particle size, shape and composition, however, most of these devices require that the aerosol is at atmospheric pressure. At the same time, many important industrial processes involving aerosols operate at elevated pressure. Thus, a sampling system is needed that can reduce the pressure of a sample stream to atmospheric pressure without sample bias due to particle losses or generation. In this work, we present the design and testing of such a device, a pressurized particle sampler (PPS) for sampling pressurized aerosols. To obtain a representative sample, the PPS utilizes: 1) two-stage dilution to minimize particle generation in the sampling probe, 2) a pressurized PM10 cyclone to remove large particles, 3) a sonic nozzle connected to an axisymmetric expansion chamber to depressurize the aerosol sampling stream with minimum impaction losses on the walls, and 4) an isokinetic sampler after the expansion to extract the aerosol to the instrumentation at atmospheric pressure. The performance of the PPS is compared with that of a simple sonic nozzle, which has been used in several previous studies to investigate aerosol formation in pressurized systems. Two approaches were employed for this comparative test. First, polydisperse NaCl particles were generated at 15 bar using a pressurized nebulizer. It was found that the pressure reduction through a sonic nozzle can lead to an underestimation of the aerosol formation due to the impaction losses on the walls during the stream expansion. In a second comparison test using ash particles, the results showed that the amount of particle loss to the walls downstream of the sonic nozzle increased with pressure. The performance of the PPS was evaluated and found to be superior to that of a sonic nozzle, and then the system was employed in a pressurized oxy-coal combustor to understand the effect of coal particle residence time on PM1 formation at 15 bar. The number particle size distribution of PM1 was found to exhibit two distinct modes, an ultrafine and an intermediate mode; however, with increasing residence time, the peak in the ultrafine mode decreased, and the peak in the intermediate mode declined steadily, and eventually becoming independent of residence time.

Copyright © 2021 American Association for Aerosol Research

抽象的

许多复杂的仪器可用于获取有关气溶胶粒径，形状和成分的详细信息，但是，大多数这些设备都要求气溶胶处于大气压下。同时，许多涉及气溶胶的重要工业过程都在高压下运行。因此，需要一种采样系统，该采样系统可以将样品流的压力降低至大气压，而不会由于颗粒损失或产生而导致样品偏斜。在这项工作中，我们介绍了这种设备的设计和测试，该设备是用于对加压气溶胶进行采样的加压颗粒采样器（PPS）。为了获得有代表性的样品，PPS利用：1）两步稀释以最大程度减少采样探针中的颗粒生成； 2）加压PM10旋风除尘器去除大颗粒；3）连接到轴对称膨胀室的声波喷嘴，以最小的壁面冲击损失使气溶胶采样流减压，以及4）膨胀后的等速采样器，在大气压下将气溶胶提取到仪器中。将PPS的性能与简单的声波喷嘴的性能进行了比较，该声波喷嘴已在先前的一些研究中用于研究加压系统中的气溶胶形成。此比较测试采用了两种方法。首先，使用加压雾化器在15 bar下生成多分散的NaCl颗粒。发现通过声波喷嘴的压力降低会由于在流膨胀期间壁上的冲击损失而导致低估了气溶胶的形成。在使用灰烬颗粒的第二次对比测试中，结果表明，声波喷嘴下游壁的颗粒损失量随压力的增加而增加。对PPS的性能进行了评估，发现其性能优于声波喷嘴，然后将该系统用于加压的氧气-煤燃烧器，以了解15 bar时煤颗粒停留时间对PM1形成的影响。发现PM1的数量粒度分布表现出两种不同的模式，即超细模式和中间模式。但是，随着停留时间的增加，超细模式的峰下降，中间模式的峰稳定下降，最终与停留时间无关。对PPS的性能进行了评估，发现其性能优于声波喷嘴，然后将该系统用于加压的氧气-煤燃烧器，以了解15 bar时煤颗粒停留时间对PM1形成的影响。发现PM1的数量粒度分布表现出两种不同的模式，即超细模式和中间模式。但是，随着停留时间的增加，超细模式的峰下降，中间模式的峰稳定下降，最终与停留时间无关。对PPS的性能进行了评估，发现其性能优于声波喷嘴，然后将该系统用于加压的氧煤燃烧器，以了解15 bar时煤颗粒停留时间对PM1形成的影响。发现PM1的数量粒度分布表现出两种不同的模式，即超细模式和中间模式。但是，随着停留时间的增加，超细模式的峰下降，中间模式的峰稳定下降，最终与停留时间无关。超细和中间模式；但是，随着停留时间的增加，超细模式的峰下降，中间模式的峰稳定下降，最终与停留时间无关。超细和中间模式；但是，随着停留时间的增加，超细模式的峰下降，中间模式的峰稳定下降，最终与停留时间无关。

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