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High Pressure Reverse Fan Cleaning Dust Collectors

Reverse Air Cleaning Baghouse Dust Collectors Also known as the reverse blower dust collector, the reverse air cleaning baghouse collects dust which forms regularly forms into a hard 'dust cake' on the dirty side of the filter bag.  This type of a dust collector uses high-pressure ‘cleaning’ air, blown in the ‘reverse’ or opposite direction of the dust laden stream, to clean the dust cake.  Also called high pressure reverse fan cleaning, these models are continuous or ‘online’ cleaning dust collectors and mitigate the drawbacks of the ‘offline’ collectors. In these collectors, cleaning could be done continuously without interrupting the process and the numerous compartments that featured in the offline dust collectors were done away with. In a reverse fan cleaning dust collector, polluted air enters the filter bags from the inlet at the bottom and passes through the inside of the bag. Dust particles collect on the walls of the bag. A chain driven motor powered traveling manifold moves across the mouth of the envelope filter bags to provide the cleaning air. The flexing of the collecting bags causes the dust cake to crack and fall into the hopper. The reverse air stream can be used to clean one bag or one row of bags at a time.

Does your application require an online reverse air cleaning baghouse? Is it unclear exactly what you may need for your dust collection? We are a network of dust collector experts.  We represent just about all types and makes of dust collectors.  By answering a few questions, we can help you determine the right equipment.  And find you the best price. Call Toll Free 1-800-525-6018

Improvements in Reverse Fan Cleaning Collector Design

• bags need not be kept stretched by use of tension devices since filter bags are pressurized from cleaning manifold
• cleaning flow is directly related to filtering capacity of the bag.
• they have higher air-to-cloth ratio (volume of air passed through the filtering bag per unit area of the bag) than shaker collectors and thereby occupy lesser space
• they are versatile models that can be used effectively for a range of applications

Considerations for Cleaning Process

In a sixteen-bag dust collector with an inlet dust load of 100 cu.ft per minute per bag, the total flow is calculated as:

Typically in these collectors, 3% of the collector is cleaned. So, cleaning (or reverse) airflow must be at three times the pressure drop. Reverse flow required to clean one bag would be:

Flow required to be drawn by the exhaust fan to maintain 1600 cu.ft/min in the collector would be:

While considering fan selection, reverse air flow has to be considered as a different source in the system. The negative pressure in the system must be maintained for greater cleaning efficiency. When negative pressure drop falls below 10 inches w.c., an auxiliary reverse air blower helps to maintain the efficiency of cleaning air stream, and when negative pressure drop exceeds 10 inches w.c., the pressure can be adjusted by providing a slide gate in the reverse air cleaning circuit.

Care must be taken to block the bags adjacent to bags that are being cleaned because these dust particles could settle on the adjacent bags, thereby reducing the collection efficiency of the system. By blocking the flow, collected dust falls from targeted bag directly into collection hopper instead of collecting on adjacent bags.

Power requirement can be calculated as under:
3% X 3 times power drop = 9% power consumption

Variations in Reverse Blower Dust Collectors

Another version of the reverse fan cleaning or reverse blower dust collector is the cylindrical dust collectors with filtering bags arranged in a circular pattern. A rotating arm moves the traveling manifold in a circular fashion atop the filter bags. The rotating arm is also designed to cover the adjacent bags to block airflow during the cleaning process.

Applications

They are commonly used in wood dust filtering where dust loads are about 10-15 grains per cu.ft. The vent stream is generally positive. Additional positive pressure blowers can also vent into one collector. Though positive blowers are less efficient than backward inclined designs, they have their own advantages.

• Use of multiple fans divides branches of vent system with low and high pressure drops. Power draw can thus be reduced between different branches. Further system fans get activated only when specific branches are in operation. In these designs, dust cannot enter inactive branches due to the back draft dampers.
• Changes can be carried out easily to branches. For example change in airflow can be achieved by merely changing fan drive for individual branch.
• Single point collection of dust facilitates efficient disposal
• Hopper design (cone shaped) facilitates smooth flow of product to hopper outlet in comparison to other hopper designs
• These collectors can be installed on the same structures that support low pressure cyclone collectors
• Upgrading to other fabric collectors is easy with few changes in ductwork

The reverse air fan provides great flexibility to positive pressure systems. Positive pressure systems have the capability of increasing the flow capacity by increasing flow through the reverse fan. By adding heat to the reverse air fan, any requirement of additional temperature spread between dry bulb and dew point temperature can be taken care of.

Since hopper openings are at atmospheric pressure in positive pressure systems dust collection is easily achieved. Hopper openings collect wood dust easily being 16-24 inches in diameter and thus prevent bridging of wood dust on opening. The reverse air fan cleaning collectors are used in grain collection and such processes.

Fan Pulse Dust Collectors

These collectors ‘pulse’ or provide short bursts of cleaning air flow for efficient cleaning. By this method a very high percentage of dust is expelled from the bags during the first tenth of the second that the bag was being cleaned. Dampers can be opened and closed by the rotating arm during cleaning pulse flow or by solenoids, which are used in some rectangular designs. Damper opens typically for ½ second and the entire cleaning operation in the collector takes 3 to 6 minutes.

Some Advantages of Reverse Air Cleaning Dust Collectors

In these collectors the cleaning air is flowing continuously even when the dampers are closed. However, reverse fan pulse cleaning collectors use less cleaning air to clean the bags than other collectors and thus have all the advantages of continuous cleaning collectors with the additional benefit of lower power usage.

Reverse fan pulse collectors are ideal for grain and other food applications due to the gradual increase of cleaning flow in the system. Fine dust leaves at lower velocities itself and does not come into play when higher cleaning velocities are reached.

Disadvantages

Reverse fan pulse collectors have the following disadvantages:

• Limited use. High manufacturing costs for fans with both high positive air pressure and at high air flow rates
• Expensive and slow damper cleaning operations
• Reversing air fan motor operates continuously to provide pulsed air for cleaning

Variations in Air Pump Fan Pulse Collectors

A variation in air pump fan pulse was achieved by increasing pressure of the cleaning arm to 7 ½ psig and using a positive displacement air pump. The design features of this variation were:

• 8-12 inch diaphragm valves that operated faster (opening and closing) than dampers
• Adequate exhaust velocity from openings on the rotating arms that facilitated openings to be placed inches from the clean air plenum. This flexibility in location of openings led to easier adaptability in mounting various types of bags and aided easier top approach with clean air plenums
• High pressure cleaning action allowed clean air pumps to be placed next to the collector with minimal pressure drop losses