There cannot be many metalcasting processes that are less exciting than collecting dust, but that’s no reason it cannot be done more effectively. A new nozzle technology makes it possible to reduce compressed-air pressure in reverse pulse-jet baghouse dust collection, its developers say, and therefore to cut energy requirements, and still to disperse the particulates effectively.

Reverse pulse-jet baghouse technology has not changed much in recent decades. These systems involve a blowpipe positioned just above the bag, with an orifice and a Venturi scrubber at the top of the bag/cage. The process uses bursts of 100-psi compressed air, and back-flushes the filters sequentially during the cleaning cycle.

Scientific Dust Collectors’ engineering manager Brian Mathews explained in a recent report that the cleaning cycle is the most important part of dust collection because of its effect on the system’s efficiency and media life. Despite its prevalence, reverse pulse-jet technology has deficiencies, which SDC aimed to correct with the converging/diverging nozzle-based cleaning system it introduced more than 30 years ago.  This “Original” supersonic nozzle eliminated the Venturi and added a cleaning system that improved cleaning, filter life, and lowered pressure drop.

Ten years ago, SDC introduced a new converging/diverging nozzle to correct some of the remaining inefficiencies of the reverse pulse-jet baghouse. This Next Generation nozzle improved on SDC’s previous supersonic nozzle design, but Mathews explained that the generic orifice and Venturi system actually draws in a vacuum of air at the top of the bag during the cleaning pulse. The developer produced a separate report to compare cleaning effects at the top of the bag with an orifice and Venturi system, and the SDC nozzle cleaning system. It concluded that the generic orifice and Venturi system does not allow the top 18 in. of filter to be used for repetitive cleaning, rendering useless that section of media.

The Original design has operated successfully at higher air-to-cloth ratios and with a manifold pressure of 100 psig, so the developer investigated the minimum manifold pressure needed for the Next Generation nozzle to achieve comparable cleaning flow at the bottom of the bag as the original supersonic nozzle? The answer is 80 psig, and a comparison of the results are shown in the nearby graph.“The significant increase in cleaning at standard pressure, and similar cleaning achieved at a lower pressure is the result of our many years of research,” Mathews noted. “In the Next Generation nozzle, we have a better understanding of supersonic flow that has allowed us to redesign and fine tune the many facets of the internal converging/diverging nozzle. Also, we were able to review the entire process from start to finish in the nozzle and eliminate flow reducing manufacturing and fabrication issues.”