6 Steps to Optimise Reverse Jet Filter Cleaning for Dust Collectors

A commonly overlooked area of inefficient compressed air use is dust collector pulse-jet cleaning — either bag (sock) type, or reverse flow filter type. Dust collector systems are vital to many plant operations, particularly with respect to meeting both indoor and outdoor air quality standards. They are also often used to collect income-producing product. At the heart of a pulse-jet type dust collector is the proper installation and availability of compressed air.

Proper operation of dust collectors is critical to minimizing cost and maximizing system effectiveness. There are many types and sizes that use a pulse of compressed air to clear the bag or filter. This pulse is usually controlled by a timer, which may or may not have an auxiliary demand control. The timers are generally set by the operators to what they believe is appropriate for proper cake removal and bag life. A properly working demand pulse control will dramatically lower the operating cost.

Basic Operating Theory of Bag Type Pulse-Jet Dust Collectors

The dust is collected on the bag or sock, and when the cake of dust is of appropriate thickness and structure, a pulse (or pulses) of compressed air is used to hit or shock the bag and knock the cake off. This pulse may sometimes be accompanied by physical shaking. Depending on the design, reverse airflow’s may also be incorporated.

When the cake is removed correctly from the dust collector, the system removes dust from its assigned environment and has a normal bag life. When the cake is not removed efficiently, the dust collector does not always continue to remove dust effectively from its assigned environment, and the bag life can be significantly shortened. Dust collection system designs specify the compressed air inlet pressure to the manifold and pulse valves necessary for effective dust removal. Based on this pressure, the pulse valve sends a given volume or weight of air to the bag at a predetermined velocity to strike and clear the cake. The actual amount and weight of the air is dependent upon the pulse nozzle being fed compressed air at a pre-determined minimum and steady pressure.

The dust collector must receive the correct pressure (or close to it) and a steady repeatable pressure level for each pulse, particularly if timers are used to control the pulses. The operator may experiment to find the right timing sequence at a desired compressed air inlet pressure. However, if this pressure varies, the performance will be inconsistent and unsatisfactory, and it may also use a great deal more compressed air.

 Dust Collector Filter Reverse Flow Pulse Cleaning

The reverse flow filter dust collector utilizes cartridge elements that are cleaned by “back flushing” with compressed air. This momentary airflow reversal is induced by a short burst of compressed air similar to pulse-jet bag dust collectors. The compressed air is released from the storage receiver by a fast-acting, high-flow diaphragm valve. This pulse of air dislodges the accumulated dust from the element. The dust then dumps into the hopper or collector drawers.

Each pulse cleans a series of filter elements, leaving the remaining cartridges available to continue filtering the air. Each diaphragm valve typically operates one pulse-jet blow pipe. Each pulse-jet blow pipe contains a nozzle for each cartridge. As the pulse of air reaches the nozzle, it is accelerated through the smaller diameter, creating a low-pressure center, or Venturi, which pulls in surrounding air through the filter in a counter-flow direction.

How Dust Collectors Impact Compressed Air Systems

From a compressed air standpoint, the supply of proper compressed air is the same. Whether pulse-jet direct or pulse-jet reverse flow, the basic valve operation is very similar and will vary by model, brand, conditions and material.

Regardless of whether the pulse-jet dust collector is bag or filter type, the critical support system of piping, storage and controls is important for not only the operating performance and maintenance cost, but also the compressed air actual demand and its effect on energy costs.

The use of a demand type pulse control, as opposed to timer activated, allows the operation to run with optimum compressed air usage. This is commonly referred to as an automatic pressure differential pulse controller.

6 Steps to Optimise your Cleaning System for Reduced Pressure Drop

• Reservoir – Poor filter cleaning can be the result of undersized or restricted cleaning system components. It is important to make sure that there are not any restrictions starting from the compressor all the way to the reservoir. Also, ensure that your header tank size matches your cleaning requirements.
• Clean Air – Ensure better cleaning with tanks that are kept free of moisture and debris as they can substantially impact the ability to clean the filters.
• Pulse Frequency – The pulsing frequency can never be any faster than the reservoir can recover to full pulsing pressure.
• Pusling Sequence – The pulse sequence should be adjusted to ensure that newly cleaned filters do not take in dust from the neighboring filter being pulsed. Staggering the firing order helps reduce cross contamination.
• Pulse Pipes – Make sure your pulse pipes are aligned properly over filters to prevent velocity damage and loss of cleaning effectiveness. Pulse pipes can be knocked out of position during installation of replacement filters, during routine maintenance, or even when pipes were initially installed. Any of these errors could result in internal velocity abrasion and premature failure.

Choice of Filter Media – All dust types have specific characteristics and require different handling. Therefore, it is often not enough to use a plain polyester media. Purchasing an enhanced treated/coated media (for example ePTFE membrane, HO treatment or antistatic surface) often turns out to be profitable as a result of better pulse cleaning.

Some of the factors that influence the right choice of media are humidity, temperature, conductivity and acid.

As an experts in dust control, EFS can help your organisation to improve their compressed air consumption and system performance.