Improving The Cleaning Cycle In Baghouse Collectors

By Brian Mathews and Glenn Bitner, Scientific Dust Collectors

Introduction

The dust collector has been around for many years. The generic pulse jet baghouse in particular has been around since 1963 and the cleaning cycle has not changed much in over 45 years. The cleaning cycle is the most important part of the dust collector. In a generic baghouse, an orifice and venturi system are used to induce air; whereas Scientific Dust Collectors uses a converging/diverging nozzle developed in the late 1970's. The converging/diverging nozzle allows for more cleaning air to be induced into the bag compared to the generic orifice and venturi system. It is because of this that Scientific Dust Collectors can operate at higher air-to-cloth ratios, clean more of the filter bag, and provide longer filter life.

The Orifice & Venturi

A typical venturi is approximately 6 inches long and has a throat diameter of 1 ¾" and is placed approximately 2 to 3 inches away from the purge tube. A hole or orifice is put into the purge tube and aligned with the venturi. During the cleaning cycle, the compressed air at high pressure leaves the orifice as a jet of air that expands by the Law of Conservation of Momentum until the jet is the same diameter as the throat of the venturi. This seals off the flow of clean air out of the bag and reverses the direction of flow to clean or "back flush" the bag.

To effectively clean the entire bag, there is only 2 to 3 inches between the orifice and the bag so that the energy of the high pressure can be used to clean the bag. This has some shortcomings, given that this short distance is not nearly enough space to draw in the required amount of air necessary to clean the entire bag. Consequently, as the air passes through the venturi, a vacuum is created at the top of the bag, pulling in air from the dirty airside of the bag to compensate for the lack of air created from the short distance. Scientific Dust Collectors has recently conducted test to observe this phenomenon.