Problem:

• A client wanted to reduce energy costs, so it decided to recycle hot air from production back into the production floors
• Before it got there, the air was purified in dust collectors – if they had failed, unaware workers would have inhaled harmful cellulose dust
• What is more, there had been a cellulose dust explosion and fire at one of the manufacturer’s sites in the past, so the risk of an explosive dust-air mixture being returned to the production areas was unacceptable.

Remedy:

• ATEX certified dust monitors have been used on the clean air ducts downstream of the six dust collectors
• The monitors indicate when the permitted concentration is exceeded, which is a signal to the operator to change the filter cartridges
• This way the monitors protect the health of personnel and reduce the risk of explosions in the plant

In this article, we will focus only on the preventive role of dust monitors installed downstream of dust collectors on clean air ducts. This role involves detecting dust in the air returned to the production area, which is most often an indication of imminent failure of the dust collectors. This solution reduces the risk of explosion and fire, as well as health problems among workers caused by harmful dust. We will begin by describing both above-mentioned risks.

Workers’ respiratory health

Many dusts are respirable, as their particle size is less than 7 µm, which means they can penetrate the gas exchange area. Diseases caused by these dusts can lead to serious chronic illnesses that, in extreme cases, can be fatal. These include cancer or other lung diseases such as pneumoconiosis or alveolitis. The dust collection units commonly used in industry, therefore, protect the health of workers by eliminating dust directly from workplaces.

Explosion risk on filter’s clean side

In this article, we focus on a selected aspect of a major project we carried out following an explosion and fire at one of the project owner’s facilities. All the key information about this project, including an explanation of how industrial dust explosion and fire hazards occur, is described in our article “Explosion and fire hazards in industrial environments: how to protect yourself from dust. A case study.”

It is worth noting at this point that, when filtering air that contains particles of combustible and explosive dust, dust collectors are a group of equipment highly prone to explosion. It only takes one hot particle transported by air into a filter to ignite an explosive atmosphere inside the filter.

On the other hand, what would happen if filter bags did not function properly (e.g. due to being torn) and thus returned dirty, dusty air to workplaces? The aforementioned hot particles could travel with air and enter the ‘clean side’ of the filters and only then initiate an explosion. There is yet another risk when dusty air is fed in just above workstations, where it is often extremely easy to encounter a potential source of ignition, like hot machine and equipment components or, for example, a spark generated by static electricity. In both cases, when an explosion occurs on the clean side of the filters, the risk to the life and health of the workers is huge, as the explosion occurs in the area where the workers, are and they have nothing to protect themselves from it.

Dust monitors as a preventive solution to detect filter bag damage

Dust monitors installed downstream of the dust collectors on the clean air ducts detect a failure in the dust collection system and allow for immediate action to be taken to rectify the failure and replace the filter element. Not only do these monitors protect workers’ health, but they are also a solution as far as explosion prevention is concerned.

They help immediately discover new dust in the ducts conveying air back to a production area and, once a dangerous concentration of dust is detected, they trigger alarm signals that are sent to employees responsible for the maintenance and safety of machinery and equipment.

In addition, monitoring long-term dust level trends on the clean side of the filters enables the optimisation of filter bag change intervals in order to avoid downtime of the dust collection units.

Immediate return on investment

Our works covered two plants, one existing and the other in the design phase. In both cases, it was decided that hot air from production would be returned to the production area. This approach was intended to reduce energy consumption, which, with the continuing increases in the price of energy, is entirely understandable. More importantly, it is estimated that the hot air return system project will pay for itself as early as the following winter.

For this reason, we proposed that the best preventive protection would be to install dust monitors on the clean side of the filters, before the returned air is delivered to the workstations.