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What are filters and how do they operate?

A filter is a mechanism which is designed to act as an air pollution control device. They work to remove solid particulates from air and gas, which have been released by commercial processes, such as; power plants, food manufacturers and chemical producers.

Common types of filter include but are not limited to; Pulse Jet Filters, Reverse Air Filters and Shaker Filters. Each of these are formed by cylindrical bags of fabric, which are used to draw through dusty air and gas and collect unwanted particulates on their surface. This filtration process is achieved by the following four mechanisms:

Interception- This mechanism occurs when particles which are following the gas or air stream, come into contact with fibers of the filter and are thus captured and removed from the gas and air flow.

Inertial Collection- Unlike small particles which have less inertia, large particles are often unable to change direction, in response to changes in a gas or airway direction. In the presence of a fiber filter, the path of large particles will therefore remain unchanged and they will instead collide with the filter surfaces.

The Brownian Movement- is the random movement of microscopic particles as a result of their collision with fast-moving molecules . This causes a diffusion of particles which increases the likelihood that they will make contact with the filter fabric surfaces and thus be captured.

Electrostatic forces- a filtration method which removes fine particles and contaminants using the force of an induced electrostatic charge. Particles become positively charged by the friction between the air and the filter. This causes air molecules to become attached to the filter fabric as they pass through it.

What issues can affect filters?

Any issues affecting filters are likely to result in the need to replace or change the filter bag, which is most commonly provoked by either physical damage to the filter bag or an issue which impedes the permeability of a filter’s collection surface.

To understand how filter issues could affect your business, it’s important to understand why and how these problems occur in the first place, to ensure that you can prevent them from reoccurring in the future.

Industrial-filter-issues
             Common types of filter include; Pulse Jet, Reverse Air and Shaker Filters.

 

Excessive Pressure drop:

When air or gas is drawn through a filter, the filter enforces a resistance to the air and gas flow, which causes a difference in pressure, between the inside and outside of the filter. This difference in pressure is what is referred to as pressure drop, which if too high, can indicate that resistance to airflow is impeding the filters ability to draw through air.

Dirty filters are the most common cause of an excessive pressure drop across the collection surface of filters and can become a serious problem. If left untreated, over time filters will gradually collect more material, until the resistance to flow results in the filter being unable to draw through anymore air.

Filter bag life:

The need to change and replace filter bags on a regular basis can be a costly and time consuming process. Prolonging the life of filter bags and decreasing the need for replacements is therefore key to decreasing the effect of filter issues upon your business.

Air to cloth ratio refers to the ratio of air quantity to the amount of collection surface area on a filter bag. If the air to cloth ratio is high it can invoke severe stress upon the filter bag fibers and thus make them prone to damage.

Furthermore, an increase in air pressure would also require a higher than normal operating pressure drop across the filter collection surface. This would increase the need for a filter to work more strenuously and therefore shorten its lifespan.

Hopper pluggage:

In addition to issues which directly inhibit the ability of filters to work efficiently, it’s equally necessary to prevent issues affecting the structures within which the filter is operating.

Caused by friction on the inner walls, hopper pluggage and material buildup restricts the mass flow of materials. As a result, particles will bind together and form blockages, which at worst can halt the flow of material completely and implement a great deal of stress on the hopper walls.

wood-product-industry
                 Industrial Filters are commonly used in the wood product industry

How can filter issues affect production?

Efficiency: Filter problems can have a significant impact upon not only their operation but also production. A decrease in the efficiency of filtration, carries the risk of causing the necessity of emergency repairs. Unplanned filter failure can therefore be a burden and a waste of your business resources, causing production interruptions ,delays in shipments, the need for over-time wages and ultimately the loss of your customers

Quality: Furthermore, if any of the above filter mechanisms are inhibited, this can lead to a significant compromisation of quality. For example, dust emissions could attract the attention of environmental regulators, which not only poses a risk in the management of quality control, but this material is effectively wasted product and therefore money.

Traditional ways of dealing with filter issues:

Traditional filter cleaning solutions offer vast and varying methods of intensity, as well as success. However, one major flaw that they all have in common, is that there solutions are only short-term.

An effective filter cleaning service, is a process that should maximise the efficiency of filters, whilst prolonging the life of their working form. Yet, traditional filter cleaning solutions only target specific and current problems, meaning they do not prevent problems from reoccurring in the future, and in some cases can exasperate additional issues.

Reverse Pulse Cleaning Systems: operate by triggering pulses and blasts of compressed air, down the centre of a filter, which introduces an airflow in the opposite direction of the filtered air. However, the major disadvantage of this method is that a high compressed air usage will increase the air to cloth ratio and thus cause excessive wear and damage to the filter medium.

Mechanical Cleaning: is a low technology form of cleaning which relies on either shaking or shocking filters in order to dislodge particulate buildup. Either manually or motor driven by a vibrator, a major disadvantage of mechanical cleaning is that airflow must be shut off during cleaning and the intensity of vibrators can cause longterm damage to external structures such as hoppers.

                    
Primasonincs - acoustic - cleaners
                     Primasonics Acoustic Cleaners provide a long-term solution to filter issues.

Why should I use Acoustic Cleaners to solve filter issues?

Acoustic Cleaning is a non intrusive technology, which provides a long-term solution to common filter issues. Not only do Acoustic Cleaners efficiently remove dust and particulate buildup on filter collection surfaces but they also maintain and prolong filter bag life- thus proving to be both an effective and economical filter maintenance investment.

Primasonics Acoustic cleaners operate by creating a series of high energy- low frequency sound waves, which penetrate materials that have built up on filters with rapid pressure fluctuations. By using alternating frequencies, acoustic cleaners are able to target particles that have different masses and which therefore travel at different speeds.

As a result, the compacted materials will vibrate at different rates to their surrounding environment, causing them to debond from each other and dislodge from the filter collection surface. Unlike reverse pulse cleaning systems however, the Acoustic Cleaning of filters can be very beneficial to filter bag life and can lead to a significant reduction in compressed air usage.

Using an advanced sonic cleaning technique, filter bags are not subjected to the excessive shocks and weave deterioration caused by reverse pulsing. This means that filters that are cleaned with acoustic cleaners can last up to 1.8 times longer than filters that are cleaned using reverse pulsing techniques.

Furthermore, having the ability to reduce and tailor the frequency of Acoustic Cleaners to deal appropriately with different levels of filter issues. Generally mounted in the Hopper section and situated below Filter bags, this means that the Acoustic Cleaners frequency can be additionally adapted to deal and prevent, not only filter issues, but other issues such as hopper bridging and ratholing.