Filter systems for air cleaning - These are the demands on dedusters

Demands on a Deduster

In general, apart from the overall concept, there are other various aspects to consider when selecting and dimensioning filter systems. A general overview of these points is provided below, which however cannot replace a technical conversation with the filter system supplier. In principle: The more detailed the information provided to the technician in charge of the dimensioning, the better the protection that the filter system will ultimately provide. The following information is necessary for dimensioning and design.

Requirements based on the material properties of the dust

In industrial production, dusts are generated at many points that differ in their properties and hazards. For this reason, the type of dust and its hazard potential must be taken into account when selecting the right dust filter system.

What impact does the dust have on operators and production?
What are the exposure limits (classification of the OEL and what should be considered regarding cross-contamination? This categorization determines the classification of the filter system (OEB level) and thus the selection of the necessary containment measures.

Depending on how effective the substances are, the filter system itself initially serves as a containment measure. For protection during operation and maintenance, containment concepts also take effect for the filter system itself.
These include among others:

• WIP (Wash-In-Place) for cleaning the filter system from the inside
• Safe-Change for contamination-free changing of filter elements (in combination with the respective closure systems)
• Choice of dust discharge, i.e. whether a simple container is sufficient or other containment measures should be applied, such as Safe-Change or RABS (Restricted Access Barrier System) for safe changing of the dust discharge with additional barrier.

What physical and chemical properties does the dust have?
The consideration of the properties of dust is important for the design of the filter system, the selection of filter elements, and the choice of materials to be used (durability).

Requirements from the process

Depending on the industry, different requirements arise from the processes: When a filter system is used in the pharmaceutical industry, special attention is focused on containment. When used in the chemical industry, high volume flow rates are the decisive factor.

The basic requirements are briefly summarized below.

Dust content of the raw gas or the required purity value of the clean gas
The amount of dust in the air to be cleaned affects the choice of filter: For example, cartridge filters are used for greater air loading, HEPA filters for lower air loading or for higher requirements regarding the purity content of the air. Often, combinations are also used:  A pre-filter is then used as the first filter stage, and a second filter stage takes over the task of filtering the fine, often hazardous substances from the air.

Volume flow rate
The volume flow rate determines the type of filter element as well as the number of filter chambers. As the effectiveness of the filter element depends on the flow rate passing through, it is limited depending on the filter material being used. For higher volume flow rates, it is then necessary to divide up the filter into several filter elements and thus to several filter chambers.

The volume flow rate is also an important parameter for dimensioning the blower or ventilator, and the connecting piping.

Temperature of the raw gas
The expected temperature of the flowing-through air has an influence on the materials to be used: At higher temperatures, the components of the filter element as well as all other installed assemblies must be designed in such a manner that unwanted effects do not occur. Insulating the filter chamber may also be necessary to protect the operating personnel from burns, as the housing may heat up.

Sound pressure level
Regarding the sound pressure level, each operator must comply with the relevant specifications. For filter systems, the source of the noise is the ventilator. Depending on ventilator design and required sound pressure level, a sound-insulated housing, vibration dampers or even a silencer must be provided for.

Explosion protection
Explosive atmospheres can develop in some processes. The classification into the corresponding zones is specified by the operator. Appropriately tested and approved concepts are available for filter systems, which ensure that if an explosion should occur within the filter systems, the rest of the complete system will not be damaged.

Operator requirements

Apart from the process-related specifications, there are also requirements that result from the overall concept of the production plant. These may include the following criteria:

Control system
The filter system's control system can be self-sufficient or be integrated in the operator's primary control system. The type of control system used depends on the required and planned signal exchange, and is often subject to customer demands.

Housing material
The choice of housing material is selected optionally to customer requirements, and also how the filter system is to be integrated into the overall concept. Often, the materials chosen result from the process (are solvents involved? Are there GMP (Good-Manufacturing-Practice) requirements, such as in the pharmaceutical industry?)

Ventilator
As for the ventilator, the question is, whether a central system handles the extraction, or if the filter system is operated directly at the extraction location. This determines the size of the ventilator and also whether the filter system is supplied with or without a ventilator. Care must always be taken to ensure that the power rating of the ventilator is in proportion to the volume flow rate. The correct dimensioning of the piping system must also be taken into account here.

Performance measurement and monitoring options
In order to check if the filter system is operating properly and performing as intended, performance characteristics, such as separation capacity, tightness against leakage, etc., can be determined. When such tests are planned for, the filter system can be equipped with appropriate measuring equipment, such as DEHS lances, upon delivery.  Several monitoring options are possible. These should be discussed in advance with the technicians, in order to find out what makes sense for your own process.