Comparison of Scientific Dust Collectors and Generic Brands

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Internal View of a Scientific Dust Collector
Generic Dust Collectors vs. Scientific Dust Collectors

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Scientific Dust Collector Image

Characteristics of Air Jet Pulses

  • Maximum possible air jet velocity at the discharge of a plain orifice, even under ideal conditions, is fixed at the speed of sound.
  • Secondary air outside the air jet will be induced into the jet, expanding the jet volume and slowing the jet down. A higher velocity jet will induce a greater volume of air.
  • An air jet discharged into free air that allows free induction of secondary air, will expand at an angle of ≈ 15o regardless of its velocity.
  • The velocity of the cleaning air jet going into the bag must be great enough to overcome the velocity of the filtered air coming out of the bag.


Generic Pulse Jet Cleaning

  • If the air jet is allowed to expand freely as it enters the throat of the filter bags, the velocity of the air jet will decrease to the point where it is not strong enough to overcome the filtered air upward velocity and only the top few feet of the bags will be cleaned unless air jet expansion is constrained.
  • By stopping the induction of secondary air, and therefore limiting the expansion of the ai4r jet, the jet velocity stays high allowing the air jet to reach the bottom of the bag with a sufficient velocity.
  • Generic pulse jet cleaning systems use a so called "venture" to stop the induction of secondary air. Their venturi does not act to induce more cleaning air, in fact the venturi limits the induction of secondary air. That is its purpose.
  • In a typical generic collector the diameter of the venturi throat is ≈ 1-3/4". The filtered air velocity through the venturi, which must be overcome by the cleaning air jet, is high duty to this small venturi area.


The Scientific Dust Collector Difference

Scientific Dust Collectors use a patented high velocity converging / diverging nozzle, instead of the plain orifice used by generics, to generate our cleaning air jet. The nozzle geometry produces air jet velocities much greater than is possible with a plain orifice. A much greater volume of secondary cleaning air is induced by this increased air jet velocity.

As with the generic system, Scientific Dust Collectors also stops the induction of secondary air to limit the expansion of the air jet. However, instead of using a flow restricting venturi, we use the whole open area of the bag mouth to limit the secondary air induction. The larger area of the bag opening reduces the filtered air velocity coming up and out of the bag. Less cleaning energy is wasted overcoming a high filtered air velocity.

Comparison of Generic vs. Scientific Dust Collectors Cleaning Systems

The comparison below assumes the only difference between dust collectors is the method of pulse jet cleaning, venturi vs. nozzle, and the air-to-cloth ratio used. Scientific Dust Collector is operating at twice the air-to-cloth of the generic system which is quite common in actual field practice.
Generic System
Scientific Dust Collectors
Bag Length
8'
8'
Bag Diameter
4-1 / 2"
4-1 / 2"
Bag Fabric Area
9.46 ft2
9.46 ft2
Air-to-cloth Ratio
5:1
10:1
Filtered Air Volume per Bag
(5)(9.46) = 47.3 CFM
(10)(9.46) = 94.6 CFM
Bag / Venturi Throat Diameter
1-3 / 4" at venturi
4-1 / 2" at bag opening
Bag / Venturi Throat Area
Filtered Air Velocity at Bag / Venturi Throat Opening
47.3 ÷ 0.0167 = 2,832 fpm
94 ÷ 0.1104 = 857 fpm
Cleaning Air Jet Velocity at Bag / Venturi Throat Opening
High Velocity Lower Volume
Lower Velocity Higher Volume

As the above calculations show, in the generic system the cleaning air jet must overcome 2,832 fpm, a much higher filtered air velocity, even though the air volume per bag is only half that of the volume run through the Scientific Dust Collector bag. The energy required to overcome the high filtered air velocity in the generic system, is not available to clean the built up dust cake off the fabric bag. Additionally, there are other problems associated with the generic system that increase bag wear and cause uneven dust cake to build up thus reducing the efficiency of the generic collector and increasing the pressure drop of the system.

Internal comparison image

Generic Cleaning System

  • The high filtered air velocity through the venturi must be overcome by the cleaning air jet, robbing it of energy to clean the bag.
  • A lower volume of secondary air is induced by the slower cleaning air jet. There is less energy available to clean the bag.
  • The high velocity of the cleaning air at the discharge of the venturi creates a greater negative pressure at the top of the fabric bag. Dust fines are more apt to embed into the fabric blinding the bag in this area reducing the effective filter area of the bag.
  • As the air jet expands inside the bag it can impinge upon the filtering media causing " dust cake flow-out". Once dust cake blow-out occurs the cleaning pressure in the bag is relieved prematurely this reducing the cleaning effectiveness.


Internal comparison image

The Scientific Dust Collector Difference

  • Much greater amount of secondary air is induced by the higher velocity air jet. More energy is available for cleaning.
  • Lower throat velocity at the inlet of the bag does not add to the negative pressure on the outside of the bag that causes dust to migrate and blind the top section of the bag.
  • More even bag inflation pressure from top to bottom of the bag causes less wear and tear on the bags.
  • Less change for dust cake blow-out to occur since the cleaning air jet is already expanded to the full diameter of the bag.
  • Dust cake is more even and it is less densely packed providing higher filtering efficiencies at lower pressure drops.
  • Scientific Dust Collectors makes better use of the available filtering media.


Internal comparison image

Downward Air Pattern and Low Can Velocities Improve Dust Collection

Dust naturally wants to fall down out of an air stream due to gravity. That is, unless the air stream is directed upward at a high enough velocity to re-entrain the dust particles.

Scientific Dust Collector housings, with high side inlets, are designed so as to promote downward air movement and to reduce the "can" velocity. Below is an example of two dust collectors, a generic collector and a Scientific Dust Collector, showing the effects of a high side inlet. Though the Scientific Dust Collector uses only half the cloth area, our enclosures are very liberally sized yielding a slightly smaller footprint than that of the generic.

Generic Dust Collector @ 5:1 A / C
Scientific Dust Collectors @ 10:1 A / C

  • 6,800 CFM @ 5:1 air-to-cloth
  • 144 bags, 8' long, 4-1 / 2" dia
  • 1,362 ft2 total fabric area
  • Bag enclosure: 80" W X 80" D X 102" H
  • Projected Interstitial Area:
  • 6,800 CFM @ 10:1 air-to-cloth
  • 72 bags, 8' long, 4-1 /2" dia
  • 681 ft2 total fabric area
  • Bag inclosure: 65" W X 92" D X 102" H
  • Projected Interstitial Area:
  • Can Velocity = 6,800 cfm ÷ 28.5 ft2 = 239 fpm
  • Can Velocity = 6,800 cfm ÷ 33.6 ft2 = 202 fpm



Internal comparison image
Scientific Dust Collectors' baffled high side inlet, an expensive option for others, allows dust laden air to flow down and across the filter bags so dust is directed down into the hopper. Scientific Dust Collectors bags are spaced on 7-1 /2" centers leaving a generous 3" spacing between bags. Generic collectors often have only a little more than 2" spacing between bags. Generic collectors often have only a little more than 2" spacing between bags. Wide bag spacing helps to keep material from bridging between bags or hopping from row to row as each successive row of bags is pulse cleaned.


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