Filtering out dust risks

Maintaining proper dust control supports safe and productive working environments, as well as dust emission standards and regulatory compliance, while mitigating combustible dust risks and helping to safeguard workers. For instance, dust particles that accumulate in hard-to-access areas around a facility can be disturbed and generate a dust cloud with explosive potential. Should this cloud come into contact with a source of ignition, it could potentially cause a fire or explosion.

The dust generated in industrial environments can cause wear on filter media, so regular maintenance is required. By implementing effective dust filtration, businesses can protect their machinery, which prolongs the lifespan of equipment and safeguards assets. Longer filter life also means less production downtime, while reduced air consumption supports lower associated energy costs. In the absence of adequate dust emission control, machinery, processes, personnel and the surrounding environment face potential risks, and production may be forced into downtime. 

To achieve effective dust control, focusing on filter efficiency is the accepted industry norm, but how well a dust collector filter is working is only part of the equation. Exposure and emissions are two other factors that are commonly overlooked, yet they also contribute to the optimisation of dust control performance. If these two elements are not taken into consideration alongside efficiency, dust control performance is not being optimised. Exposure and emissions are two key performance indicators, and the intent of a dust control system is to stay within those thresholds. The efficiency of a dust collector and filter is the result of reaching those goals.

Exposure 

A qualified industrial hygienist can audit a facility to evaluate air quality and potential employee exposures, determining average or peak concentrations of contaminants. They will review various job functions and take air samples to provide recommendations for how to address air quality and contaminants. 

Exposure to nuisance dust in and around manufacturing processes creates discomfort and annoyance. This includes the properties of the materials produced or used in a facility, and the locations in a process where exposure to those materials occurs.

Fugitive dust is where particles become airborne from elements of an industrial process that are not enclosed or controlled appropriately. This includes any location in a facility where dust escapes freely into the air, rather than being captured by a dust collection system. 

Hooding can be an effective means of reducing exposure to dust, but only when designed effectively and properly located near the source of dust generation. An audit can identify the facility’s dust sources to verify if ventilation hooding currently in use is appropriate. This is often when new dust generation points and the need to add controls, such as additional hood locations, are identified.

Hooding and ducting 

Hood and duct design play a crucial role in effective exposure control. Dust collector performance depends heavily on how well the hoods and ductwork function together. They should capture dust and transport it to the collector without allowing settling or leakage.  

Within ducting heavier particles need high velocities, while lighter fumes may require less. Dust settling within ducts can cripple system performance, leading to blockages, structural load issues and reduced airflow, while excessively high velocities can raise energy usage and accelerate duct wear.  It is therefore essential to check that there is a logical network of ducts to convey the dust or fumes from each hood to the collector. Ducts must also be sized properly so that recommended minimum conveying velocities are maintained, and that air volume is sufficient to keep the dust moving to the collector. 

It is also important to think beyond hood size. A dust collector can only filter the air stream that is brought to it, so if the hood captures 20% of the dust, the system will perform at a maximum of 20% regardless of how much is invested in other components. Hence it is necessary to review existing exhaust hoods to determine whether they provide sufficient control volume or if modifications are required.

Efficiency

Once exposure areas have been addressed, the next step is to review appropriate dust collection technology. A dust collector should deliver consistent and predictable performance that effectively removes contaminants, while maintaining a consistent air volume at a predictable energy cost. The size and style of a dust collector will influence the fan and cleaning energy necessary for stable operation. This means developing the most efficient system to deliver the required air volume. If your system struggles to maintain design flow, or cleans excessively, it may mean that an investment in new technology is warranted.

When assessing the appropriate dust collector, is also important to analyse the type of filter and the filter efficiency. Unfortunately, it’s not as simple as looking into filter ratings, as these are tested under lab conditions and don’t always relate to a facility’s individual needs. For example, a filter rated ePM 2.5 simply means that it captures about >65%of test dust under specific conditions, rather than the particular conditions experienced in individual plants.

A filter in a regenerative dust collector is often pulse-cleaned under heavy loads. It must handle new dust entering the collector, in addition to all the dust accumulated on the filter over time. When a dust collector reaches a stable operating point, the dust concentration on the filer media is thousands of times greater than the inlet loading. Evaluating a dust collector in terms of what it achieves at its stable set point, and using exposure and emissions testing will give a better indication of the ventilation system’s performance.

Emissions 

Outlet emissions are what passes through the dust collector. It is therefore important to know the quality of the filtered air being emitted back into the building or exhausting outside. 

Questions to ask therefore include: 

• What besides filtered air might be present in the airstream? 
• Are there remaining particulates, vapours, or gases? 
• Do any of these questions pose a concern? 
• What further actions are necessary?

Answers to these questions requires systematic testing to monitor air quality. An air quality monitoring firm can perform stack testing to measure outlet emissions against air quality goals. Stack testing measures the volume and concentrations of material discharged at the outlet of a collector. 

For some facilities, industry-relevant regulations mandate continuous emissions monitoring. This is not a comprehensive list, but examples include the Environmental Permitting (England and Wales) Regulations 2016 – the primary framework mandating dust emissions monitoring. The requirement for Continuous Emissions Monitoring Systems (CEMS) for dust (particulate matter) is typically not explicitly written into the main body of the Regulation but is a condition of the Environmental Permit issued to each installation. The core European Union regulation that mandates continuous dust emissions monitoring for large industrial installations is the Industrial Emissions Directive (IED). In the USA, regulations mandating continuous dust emissions monitoring are primarily established and enforced by the Environmental Protection Agency (EPA) under the authority of the Clean Air Act (CAA). Other application- and industry-specific local, national and international standards may also apply, dictating the need for a variety of test methods to determine emissions or exposure limits. 

A complete approach

Once ventilation needs and emissions limits are understood, a qualified industrial ventilation designer can produce a suitable dust collection system. They will identify what the dust load demands may produce in terms of energy and cleaning consumption, and how to achieve emissions goals in both a cost and energy efficient way. For example, one set of equipment may deliver reasonable filter life at a lower initial cost but have higher compressed air and cleaning costs due to aggressive filter sizing. Meanwhile, a more conservatively sized dust collector will have a higher initial cost, but lower compressed air and energy consumption due to less frequent filter cleaning. Likewise, less frequent filter cleaning leads to lower outlet emissions.  

Whenever changes are made to a facility or process, it is also important to remember that any resulting modifications to the dust collection system can throw the system out of balance in terms of air volume throughout the system. For example, tapping into a system with another duct may create a path of lower resistance that diverts air from the original sources. An industrial ventilation designer can advise on system modifications, while retesting for exposure and emissions will verify that the remodelled system is performing as designed.

Controlling industrial dust is an essential part of a facility operator’s overall EHS (Environmental, Health, and Safety) programme. The three key factors that should be taken into consideration are exposure, emissions and efficiency. Appropriately designed hooding and ductwork that captures dust directly at the point where it is generated is a key part of addressing exposure. Emissions, which are typically subject to regulatory requirements, serve as a useful measure of the quality of air being filtered. With both of these elements under control, attention can then turn to the overall efficiency of the dust collection system, ensuring it continues to fulfil its vital role in safeguarding workers, equipment and the environment.

Nicolas Van der veken is product manager at Donaldson. For more information, visit, www.donaldson.com